Building and modifying
Many people successfully build their own camper trailer. Doing so requires some engineering and design skills, proficiency with hand tools and ideally experience as a welder. The latter can be acquired at TAFE, but needs practice before you do it well. Obtaining that practice by building a trailer you may then take into the outback is not the best way to acquire it. Unless you are a truly experienced welder, seek help where needed.
A vital resource is VSB-1 (National Code of Building Practice ‘Building Small Trailers’). It is updated from time to time. Ensure you have the current one.
The Code’s general requirements are Australia-wide with very minor state to state differences. The main trap for camper trailer builders is that entry door/s must open outward. Most owner builders report few registration problems as long as the requirements are established before starting, and then closely followed.
Make up a scale drawing that includes the location of all major masses. Keep these low down and as close to the axle as possible. Draw up a table of estimated probable weights before starting construction as it is only too easy to end up overweight.
Australian-built caravans typically have 10% of their overall weight as tow ball loading, but 5-6% is adequate for camper trailers as they have far lower forces that cause trailers to yaw and pitch.
Your drawing and table enables you to assess axle placement but you’ll need to do some arithmetic as tow ball weight relates to the tow hitch coupling’s distance from the axle.
The major loads are caused by pitching. They may cause the chassis to flex where the front of the trailer body begins. Triangulate this area, or run a steel truss below it.
Many trailer makers mount heavy stuff on the drawbar – imposing stresses that must be counteracted by increasing strength. That, in much of the industry, results in disproportionately increasing weight. It also results in unnecessarily high tow bar loads that restricts your choice of towing vehicle and also limits its payload.
For a thorough explanation of all this, see https://rvbooks.com.au/caravan-and-tow-vehicle-dynamics/
Front of author’s previously-owned Tvan was rebuilt in marine alloy. Inbuilt stone guard deflected stones downward. Pic: RV Books.
Many commercially-built camper trailers seem absurdly heavy – yet do not need to be. Here are three examples of exceptions.
The Ultimate weighs about 850 kg (and has a ball weight of 40-50 kg).
The Tvan weighs 780 kg. I rebuilt the front using marine grade aluminium – reducing it to 730 kg.
Western Australia’s Australian Swagman used aluminium and weighed under 600 kg.
Lightness and strength really can be combined (all three are truly off-road units). It is readily possible to build a camper trailer this way – i.e. by not confusing weight with strength.
Avoiding excess weight is essential if you travel extensively off-road because inherently heavy items such as water cannot be reduced below safe levels. Excess weight also increases fuel consumption.
Whilst hardly camper trailers, and not for off-road use, an example of what is possible, are the ultra-light fifth-wheel caravans built by Glenn Portch. His lightest, a 10.2 metre unit, was about 2800 kg.
Chassis construction is reasonably straightforward but you will need an engineer’s certificate of road-worthiness (the local registration authority will advise).
Most trailers have the chassis formed from RHS (Rectangular Hollow Section) Duragal. This is springier and 30% stronger than normal steel. Typical chassis use sections up to 100 mm by 50 mm, but cheap (especially kit) trailers may use folded up 50 mm C section – often of low grade steel.
A few camper trailer makers produce alloy chassis, but mostly as if in steel but with heavier sections. It is too early to comment on their long term off-road usage but it seems pointless unless lighter.
A box-like frame is usually fabricated from 25 mm light gauge SHS (Square Hollow Section) clad with galvanised steel sheet or (sometimes) aluminium.
The end result is rugged, relatively easily repairable, affordable, but (even clad with aluminium) is extremely heavy. Some weigh as much as a 4WD. A lighter approach is preferable.
Another approach (for on-road units) is to use one of the AL-KO range of lightweight short caravan chassis that are supplied with the rubber suspension described and shown below.
A simple and effective approach is to use a really well made beam axle and ex Hilux rear springs with one or two spring leaves removed.
AL-KO suspension units are partially self-damping, but the optional shock absorbers are advisable for off-road use. Pic: AL-KO Europe.
Coil sprung independent suspension units are commercially available. It may pay to use one rather than building your own as most are well designed and engineered.
Coil or leaf springs should be selected such that they deflect about 35-40 mm when the trailer is fully laden. Include top quality shock absorbers.
Another solution, AL-KO’s rubber suspension units, bolt to the main chassis members. They are available for various loadings. With these, shock absorbers are optional (as rubber is partially self-damping) but recommended for off-road use. It is essential to use the size AL-KO unit that is applicable for the laden weight of your trailer. This is not that hard to do if you keep track of weight as you build – and allow for that of all that you intend to carry. If building an off-road unit, choose the next larger AL-KO suspension unit than for on-road use.
Hardly a camper trailer! – but Glenn Portch’s ultra-light alloy space frame ‘chassis’ of his 11.3 metre fifth wheeler may give camper trailer builders a few ideas. Pic: Glenn Portch 2010.
Chipboard and MDF is heavy: 20-30 kg/m². It has close to zero strength and falls apart if wet. Do not even think of using it. Marine quality plywood of adequate strength weighs about 8 kg/m². Aluminium sheet is a good light material and looks wonderful when powder-coated. Composites such as Lucan, or aluminium honeycomb, are light and work well, but need skill to employ.
If doing so, consider using Sikaflex 252 to hold it all together, but experiment first. Use guides to ensure all is positioned accurately first time because the product holds like chewing gum once parts touch. It has a tensile strength of 4000 kPA (580 psi).
This compound remains slightly flexible, allowing slight movement that usefully reduces local stresses and cracking. Additional fastening is neither necessary nor desirable. OKA’s mining truck bodies were built this way. Instead of canvas, save weight by using the material made for enclosing open-sided trucks. It is ultra-strong – thus enabling larger openings for screens etc.
Caravan equipment suppliers stock plastic water tanks, often of recycled material. They are light and affordable, but the material is very thick resulting in the tanks taking up valuable space.
Stainless steel tanks are light and strong but must be well supported as they are prone to fatigue cracking. They can be custom-made, but prices vary considerably.
Include breathers to allow air to escape whilst filling. These need to be of at least half the area of the filler pipe with outlets well above the top of the tank. Outlets tend to block so need to be removable for cleaning. You will know when this is required by bonging noises from the tank/s, and water spurting back when you refill.
Protecting the underside
Few builders (commercial or otherwise) address the damage done to the underside of an off-road trailer by stones and rocks thrown up by the towing vehicle. It is subjected to ongoing battering.
Galvanising steel bits (or using Duragal steel) assists, but is better reinforced with one of the brush-on bitumen compounds made for this purpose – and redone every year or two (Ultimate does this.) Powder coating looks good in the showroom but will be blasted off the vulnerable bits within hours.
Protect hydraulic brake hoses and brake cables plus all wiring – preferably by shields that deflect rocks and stones.
Protect shock absorbers by steel deflectors. Don’t cover them with any form of foam as that will cause them to overheat and fade.
Mesh stone guard (on Cub Camper). Pic: Bob Lynch.
Add a mesh stone guard to prevent stones from the tow vehicle being bounced back and through that vehicle’s rear window.
Alloy can be used but mesh is cheaper, and more effective.
Building your own fridge
Consider building your own fridge to fit available space. It makes sense as it can be the size and shape you wish. DIY kits are supplied by Engel, Sea Frost (USA) and Waeco.
All enable the Danfoss compressor to be remote from the fridge compartment.
The Sea Frost product is used extensively by sailors for whom building a fridge is routine. That, and similar systems consist of two components, the compressor and a stainless steel cold plate.
Cooling efficiency depends on the quality and thickness of the insulated ‘fridge’ part of the system (best made as chest top opening).
Installation is easy. The system takes fan-drawn outside cool air and exhausts the warm air to atmosphere via flexible tubing. For fridges, the cooling plate/s take up about 20% of the inside surface area. For fridge/freezers, however, that area may be about 60%.
Typical Sea Frost compressor section: approx. 200 x 200 x 400 mm, and 9 kg. Pic: Seafrost.
Sea Frost states that 77-100 mm thick top quality insulation enables, in tropical climates: ‘Fridge capacity 65 litre, current consumption approximately 25 amp hours/day. For 225 litre – 57 amp hours/day, and for 440 litre – 70 amp hours/day.’
Whilst a lot of energy is required for the initial content cooling, there need only be minor energy losses thereafter.
The overriding rule (in Australia) is that gas installation or gas maintenance work shall only be undertaken by a licensed gas fitter. Installation and usage must conform to AS 5601:2 -2012 (Gas Installations). Reinforced glass-fibre cylinders are light but costly. Some are see-through, enabling the liquid gas level to be checked.
Diesel cook top
The weight of a gas cylinder can be avoided by using a diesel powered cooking top. Webasto has one marketed under its own and other brands. They are clean, silent and not smelly in use. An alternative is the Origo acohol-powered range of cooktops marketed in Australia by Dometic.
ADRs (Australian Design Rules VSB-1) specify the wiring needed for the obligatory on-road lights. It makes sense to install all of the 12 volt wiring to these requirements.
These include: cables be anchored to the chassis at intervals of not less than 600 mm, cables be insulated at all joints and located such that they cannot become overheated nor contact moving parts, and protected from chafing.
An earth wire must be provided between the trailer and towing vehicle. It is not sufficient, nor acceptable, to use the trailer coupling as an earth (i.e. via the tow ball or whatever). Don’t mess about with the on-road electrical bits. This is auto-electrician territory.
Wiring within the camper trailer runs from battery voltage. It needs the larger sized cable described and specified on many pages throughout this book.
Early trailers had six pin connectors. Those made from 1982-1985 usually have a seven-pin device that accords with the earlier AS 2513. Later ones may have a flat twelve-pin connector. Those meeting that standard are mainly from Brylite, Hella and Utilux. Identical looking imported connectors did not necessarily comply. AS 2513 is about electrical issues – not of shape. Some plugs and sockets were flat, others round. Several different types are in use today. Adaptors enable you to temporarily tow a trailer that has either type of connector, or your own via a different vehicle.
Sanity set in with AS 4177-5-1995. This specifies a flat twelve-pin socket that accepts both flat seven-pin and twelve-pin plugs. Go for the twelve-pin Type 3 connectors – or the latest 13 pin version.
Front & rear reflectors. Two white non-triangular reflectors must be fitted to the front, plus two red reflectors to the rear. Dimensions (front and rear), A: 350 mm minimum, B :900 mm minimum. C: 150 mm maximum (equidistant about centre line). Reflectors must comply with ECE R3/-.
Tail Lights. There must be two red lights. Dimensions. A: preferably 1500 mm high maximum (2100 mm maximum if body shape dictates). B: 350 mm maximum. C: 600 mm minimum (equidistant about the centre line). Lights must comply with ECE R3/-.
Stop lights. Not less than two. All must show red. If the trailer has independent brakes these lights must be displayed even if the trailer brakes (only) are applied. Dimensions. A: 1500 mm maximum. B: 350 mm minimum. C: 600 mm minimum (equidistant about the centre line). Lights must comply with ECE R7/-.
Direction indicators. A direction indicator light must be fitted to each side of the trailer. Note the interelated positioning. Dimensions. A = 1500 mm maximum (or 2100 mm if body shape dictates). B – if distance E is <300 mm, then distance B must be less than 50 mm D = 350 mm minimum. Lights must comply with ECE R6/-.
Number plate light/s. There must be at least one number plate light that must illuminate that plate. There may be one light at either side of the number plate, or a single one at the top. Light/s must comply with ECE R4/-.
Rear (combinations). One of many permissible groupings. All lights and reflectors must be within the dimensional limits indicated. Here, A: direction indicator/hazard lights. B: stop lights. C: rear position lamps (side lights). D: number plate lights. E: reflectors.
Wide Trailers. For trailers over 1600 mm wide, two front lights are required. These must be white (or amber if doubling as side marker lights.) Dimensions. A: = 1500 mm maximum, or 2100 mm maximum if shape dictates. B := 350 mm maximum. C: = 600 mm minimum (equidistant about the centre line). Lights must comply with ECE R7/-.
Long Trailers. There must be an amber coloured side reflex reflector within 3 metres of the front of the trailer (including drawbar) and a similar reflector within 1 metre of the rear of the trailer. These reflectors must not be more than 3 metres apart. A further and similar reflector must be positioned at the middle third of the trailer (including the drawbar). Dimensions, A: = 3 metres maximum. B: = middle third of trailer (including drawbar. C: = 1 metre maximum. D: = 30 mm minimum. E: = 900 mm maximum (1500 mm if shape dictates). Reflectors must comply with ECE R3/-.
Unless stated otherwise, trailer lights must operate at the same time as the corresponding lights on the trailer. Paired lights and reflectors must be equidistant either side of the centre line. If your trailer is over 2.1 metres wide, and or 7.5 metres long you’ll need to include end-outline (clearance) lights: two white end-outline lights at the front and two red end-outline lights at the rear.
Shown below are connections for round seven-pin sockets, and both seven-pin and twelve-pin flat sockets (as seen from the wiring side). Pins 1-7 are rated at 15 amps for 30 minutes. Pins 8-12 of twelve-pin sockets are rated at 35 amps. Some local makers use pin 2 (of seven-pin connectors) for auxiliary lighting – precluding using reversing lights. This appears to contravene the Design Rules but is common practice.
AS 2513 and AS 4177-5 recommend pin 5 be reserved for electric brakes. Check this, as brand-new trailers have had their brakes to burn out within an hour or so of connecting up because the installer wrongly used pin 5 of the towing vehicle’s socket as a permanently-on 12-volt supply to the trailer.
Brylite and others make four-pin plugs and sockets for loads such as three-way fridges, battery charging etc. Anderson plugs and sockets are also increasingly used for this.
Standard pin numbering and cable colour – seen from the wiring side. See main text (above) re often incorrect use of pin 2 of 7 pin connectors. Note that contrary to general convention, white is used for chassis and earth. Some Australian states used varying connections for early 7-pin connectors.
7/12 pin connections
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