Self Build Guide - 4. Chassis and Suspension

This is part of our self-build caravan series. This section looks at the chassis and suspension choices before you build the caravan body.

The chassis is one of the biggest decisions in a home build because it affects weight, suspension, floor height, registration, braking and long-term durability. Treat the measurements and examples below as practical guidance, not an engineering certificate.

For the full series, start with Ever Wanted To Build or Rebuild a Caravan?.

1. Choosing a chassis path

The caravan chassis is perhaps the biggest hurdle home builders have to overcome. There are three main ways to tackle it:

• Build your own chassis from scratch if you are already a competent welder and understand trailer construction.
• Have a professional chassis builder make one to your layout and weight requirements.
• Reuse a suitable old caravan chassis after carefully checking condition, brakes, suspension and compliance.

The best option depends on your skills, budget, tools, intended travel and how much risk you are prepared to carry. If the chassis is wrong, every later stage of the build becomes harder.

2. Build your own from scratch

If you are already a competent welder then you can probably build the chassis yourself. We can explain the basic principles and materials, but you need to study the design of a commercial caravan built for the conditions and loaded weight you expect to run.

Axles and suspension can be purchased and attached, but the chassis still needs to be designed around the finished van weight, axle group, tow ball weight, tank positions, floor support, body mounting points and expected road use.

If you are nervous about building your own chassis, that is a good instinct to listen to. There are other options.

3. Pay a professional to build it

There are professional chassis builders around. You will usually find them by searching within your state or capital city. If you are unable to source a ready-made option, you could measure up an existing similar-quality chassis and provide drawings to a welder or trailer builder.

There are also some standard chassis available from trailer manufacturers and online marketplaces. A standard chassis can save time, but it still needs to suit your intended body size, axle position, suspension, coupling, brakes and loaded weight.

The advantage of a professional build is that you are not learning welding, design and compliance at the most critical part of the project.

4. Reuse an old caravan chassis

Another option is dismantling an existing caravan for the sole purpose of building on the existing chassis. This can give you the option of changing the layout and reusing some components and materials.

The two main advantages of this approach are:

• You are using a proven chassis.
• As you dismantle the caravan, you can examine how it was put together and in what order.

This reverse engineering should not be underestimated. Resist the urge to demolish the cabin just to get to the fun part of building.

The disadvantage is that some very old caravans may have brake systems that are no longer suitable, or the chassis strength may not suit the popular outback-style build. If your intention is to get to more remote areas, a complete custom build may be the better answer.

5. Suspension and axles

You do need a good strong suspension system, but that does not mean it has to be the fanciest or most expensive.

Many modern off-road caravans have independent suspension. In my experience it can be more of a marketing feature than completely necessary. I will not try to talk you out of one, but if money is limited you may be better off choosing a high-quality rocker roller spring and solid axle setup rather than a cheap independent system.

One of my greatest worries is breaking a specialised suspension component in the middle of nowhere. Leaf springs are much easier to understand and repair in remote areas.

Do not use slipper springs on a caravan. They are cheaper but are best reserved for on-road camper trailers.

My latest personal van has rocker roller springs and solid axles. It recently did the Gibb River Road with no issues.

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6. Standard design and materials

My current caravan is 20 feet long and semi-off-road. The chassis was based on a Roadstar caravan.

The main material sizes are:

• A-frame: 150mm x 50mm RHS, 3mm thick, with a lower offset tension strap 30mm x 5mm.
• Main longitudinal chassis rails: 100mm x 50mm RHS, 3mm thick.
• First half of chassis rail: additional 100mm x 50mm RHS welded under the main chassis rail.
• Behind the full suspension mounting: 3000mm long, 100mm x 6mm flat bar welded to the inside face of the main chassis rail.

The cross members between the chassis rails are:

• 50mm x 50mm RHS x 1.5mm for each floor sheet join.
• 50mm angle x 3mm for intermediate floor supports.

The outriggers protrude outwards from the main chassis rail to the wall supports:

• Outriggers are as above.
• Floor side support is 25mm x 3mm angle.
• Wall supports are short 50mm long, 25mm x 3mm angle.