Which caravan construction is best?

Caravan bodies are divided roughly into two types, aluminium/timber and composite, but which is better?

Back in the 1990s, just about the only new caravan you could buy was one with an aluminium-clad timber frame sitting on a heavy box-section chassis. ‘Stick and tin’ as they call it in the trade…

Since then, the Europeans arrived with their monocoque-frame, lightweight caravans, where the composite body sits on a lightened chassis because the body itself is very rigid.

So which one is better? Like so many things, there are pros and cons for each.

The earliest caravans from the 1930s had plywood bodies (often referred to as bondwood, a trade name used by Boral) built on steel chassis.

By the 1960s, the aluminium sheet, hardwood frame body on a steel chassis had started to be become popular and has been the mainstay of Australian caravan production since.

Most traditional-build Aussie vans are based on a chassis that has 100mm x 50mm RHS main rails -- nice and strong (and heavy) for our rough roads. There are smaller-diameter lateral (and often longitudinal) box-section steel supports and suspension is typically a leaf-spring set-up.

On top of this is (usually) assembled a plywood floor and timber frame -- Meranti timber the most popular because of its light weight and strength.

Polystyrene insulation is then fitted in between the timber sections, then the corrugated aluminium sheeting attached.

The van’s side sheets are fitted in an overlay fashion, from the bottom up, whereas the front, roof and rear sections are typically in long sections as the manufacturer can use U joins to connect them together.

Some manufacturers in the 1970s such as Viscount used aluminium instead of timber to make its frames, while Millard continues to use that method today, as does Coromal.

Then, in the early 2000s a wave of European vans arrived, which used a very different approach to caravan building.

Their chassis and body construction – which has continued basically unchanged – was much lighter and simpler than in Aussie vans, and often they just C-section chassis rails and A-frames.

The reason the Europeans could get away with such a light, and less rigid chassis is because of their body structure. The floor, walls, roof and front and rear sections were each one-piece fibreglass (or aluminium) composite panels interlocked together.

The result was a very rigid body – and one that was very light too. There was no need for a heavy chassis to support it because the body itself was so strong.

The pros and cons

So what are the advantages and disadvantages of each construction method?

The Aussie approach may have resulted in a rock-solid chassis that could handle just about any rough road it was hauled over, but the weakness in this design comes with the extra weight of such a chassis.

Then the body structure itself can have problems. With the numerous joins in the external aluminium sheeting, over time water leaks can become a problem – and with water soaked into it, eventually the timber frame rots.

In fact, Danie Johansson of Complete RV Services in Penrith NSW said that it’s a common problem with aluminium-clad vans.

“Ninety per cent of the aluminium-clad vans we’ve had in this year for panel/cladding repairs have had evidence of prior water ingress,” he said.

The thin aluminium sheeting is also more vulnerable to damage, whether it be from hail or being scraped against a solid object.

If you need to replace the sheets on an older van, finding painted aluminium sheeting that matches the van’s original colour can become difficult.

The composite caravan has its weight-saving mostly in the chassis – it doesn’t need to be strong here because most of the strength is derived from the body structure.

The traditionalists argue that the Euro van chassis is not strong enough for local conditions. There might be something to that, because most composite van manufacturers – whether overseas or local – use a strengthened chassis compared to the Euro market vans.

Yet ask owners of German brand Geist caravans, which were sold in effectively Euro-spec (in respect of chassis structure) here until 2008, about durability and they are almost wholeheartedly positive about how well their vans are holding up, even now.

The frame sections in the composite body (and by that we mean walls, the roof and often the floor) are made of fibreglass or aluminium sandwich panels. The frames interlock to form a strong structure, with joints enclosed in aluminium channels. The frames are then screwed together but also bonded – not with any old glue but a polymer glue (also used in automotive manufacture) that’s very strong.

The net result is so strong that Avida – one of many local manufacturers who have adopted the Euro body structure concept – demonstrated this by putting one of its caravans on top of another.

Like some of its local competitors, Avida employs elements of both European and local caravan construction methods. The body is Euro-inspired, while the chassis is stronger than the typical European van. Avida still uses techniques to keep chassis weight down, such as using fewer lateral chassis supports.

Composite can be cheaper to repair

So the composite-body caravan is lighter and stronger and theoretically, less prone to leaks and if they occur they will not compromise the body structure. The hard composite shell is also far less prone to damage from hailstones or minor knocks.

If the composite body is damaged, Johanson said that doesn’t mean that whole sections must be replaced.

“If it’s done in the correct manner, you can do section repairs. In Europe, they’ve never changed a whole wall for localised damage; they do section repairs,” he said.

“Minor dents, gouges and so on can be filled as they would for a motor vehicle repair, which makes for a very cheap isolated repair.

“Cladded vans need all the sheets below the affected area removed to gain access to the damaged sheets – when the van is built, the aluminium cladding is installed from the top down.”

So if, for example, the whole side wall needs to be replaced, – which given the above, would apply to either an aluminium-clad van or a composite – you (or your insurance company) don’t get a bigger bill to fix the composite.

“If a wall is badly damaged and needs to be replaced, there’s not much difference in cost between an aluminium-clad van and a composite,” Johanson said.

If the damage is not the result of a sideswipe but an impact, then Johanson said the composite structure can be quicker and cheaper to fix.

“If it’s had a major shunt in the side, with a sandwich construction wall you just replace it; you don’t have to strip the frame and repair it like you do with an auminium-clad van.”

Which caravan construction is best?

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