The truth about composite caravans

The Australian RV industry has gone though a bit of a revolution over the past five to 10 years; slowly but surely, the traditional 'stick 'n tin' construction that has been with us for more than 50 years is being gradually replaced by composite construction caravans, campers and motorhomes.

The old construction method was to build a (usually Meranti) timber frame (or, in some cases, aluminium frame) over a very solid steel chassis. Then the timber would usually have styrofoam insulation inserted between the framing sections, and the lot would be lined on the inside with plywood and finished off with corrugated aluminium sheet cladding on the outside.

Then it was glued and screwed onto the timber frame (or pop-riveted if aluminium) and sealed with mastic or more recently silicone sealer.

RV holy grail?

The new, composite structure has far less joins and is (theoretically) lighter, stronger and does not – in theory – require such a strong, heavy chassis to underpin it like a timber frame caravan does. The body becomes a structural member of the RV, as it's very rigid and strong compared with a timber frame.

The typical full composite structure has one-piece floor, side walls and roof sections with aluminium C-section joins holding the main structure together as well as silicone and screws. The interior furniture is pinned/glued to the inner walls, which add to the rigidity.

But does the latest composite structure stack up as the holy grail of RV construction? That depends on what exactly is meant by ‘composite’. There are basically three key types of composite in RV construction.

Most common composites

The most common composite ‘sandwich’ panels consist of a fibreglass, aluminium, reinforced thermoplastic or plywood outer sheet, extruded polystyrene (XPS) or expanded polystyrene (EPS) foam cores, and reinforcements and frames in polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyurethane (PU), aluminium, timber or plywood.

The composite sandwich panels we see in Aussie caravans, campers and motorhomes can be up to 40mm thick, although slightly thinner and therefore lighter panels are used on many British and European vans due to smaller tow vehicles used and limited off-road use.

There's another type of composite, that's not the 30mm to 40mm thick, rigid sandwich panels as above, but more like a replacement for aluminium sheeting on a timber or aluminium-framed RV. Adopted by many Victorian caravan manufacturers in recent years, this 3-4mm thick ‘composite’ (with thin inner and outer aluminium skins encasing a polyethylene core) is more commonly used for street signs and building cladding.

As discovered tragically in a London apartment block a few years ago, this type of cladding isn’t necessarily all rated to withstand fire. The cheaper examples of 3-4mm aluminium skin composite are also far more prone to delamination. The material can work really well in some builds, but you have to be certain of its quality and fire-resistance in an RV application.

Aussie toughness adds weight

The thicker sandwich panels used on many Australian vans are not only heavier than on the Euro vans, but also often 'stick and tin' construction. So depending on the particular build, the weight saving advantages of a composite van can end up being negligible.

Australian composite caravans, especially so-called off-road models, also have a stronger, heavier chassis than many Euro vans, again negating the theoretical weight advantages of composites. In fact, some are even heavier than a similarly sized and equipped timber-frame, aluminium-clad caravan.

On the plus side, fibreglass outer sheets generally have good hail resistance, whereas aluminium- outer-skin composites – much like old-school aluminium sheet RVs – are more easily damaged by hail.

Although not subject to rot as a timber frame is, a poor-quality outer composite skin RV can still delaminate under Australia’s harsh UV conditions.

Repair costs

One of the advantages of composite construction – fewer sections than aluminium sheet cladding, and therefore fewer joins and potential leaks – can turn to a disadvantage if the RV is damaged.

If the damage is in only a small area, some composites can have a sectional repair done, although even this is pretty specialised work. The repair can be more complicated with some European RVs that have a stucco outer finish – this requires special equipment at the repair site to replicate the finish on the bare, replacement composite section.

However, it gets even more complicated if the damage is widespread. For example, if you were to be unlucky enough to scrape much of the side of a composite panel caravan along a tree or a post, it will require the whole side panel to be taken off and replaced. That is a big, time-consuming job, as you're also dealing with removing the bonded wall from furniture and replacing windows and possibly a door as well.

Depending on where the damage is (the higher the better as the sheets are layered from the bottom up), a scrape all down the side of an old-school aluminium-clad RV could be repaired in a matter of hours. The principle of having many outer sheets can work in your favour when replacing them quickly and cheaply in this case.

Replacing panels

Even if the damage is more widespread with a stick 'n tin RV, the repairer can do the timber and aluminium cutting and measuring on the spot. While in a sense it's customised work with a lot of measuring and cutting that requires a higher level of skill on the part of the repairer, it's often a quicker, easier repair job overall. The materials are more easily sourced, transported and stored too.

On the other hand, a precise, CNC-cut complete side or roof panel replacement will need to be supplied as a spare part by the RV manufacturer, and it's not necessarily the case that the RV manufacturer or supplier will have exactly your caravan model’s complete side or roof composite section in stock, all CNC-machined and ready to go.

Some local sandwich panel manufacturers can supply the section needed, precisely cut to your measurements, but they don’t tend to do window cut-outs and the like. This adds time and complications for the repairer, who may prefer to not take on such a difficult job.

It can also cost more to ship the panel, because it's more bulky than sheets of aluminium or lengths of timber, and the repairer may require more workspace to store the panel before doing the repair.

Even though a full composite RV has fewer joins and doesn’t flex as much, that doesn’t mean it will never leak or need sealant maintenance like a stick 'n tin RV.

The join sealants used in a composite RV are subject to the same UV degradation over time as a traditional timber frame van. The silicone will eventually start to peel away and water will find its way inside.

It’s hard to give an exact time of how long the sealant will last, but after several years of sitting in the weather and being bounced around highways and byways, the sealant will definitely need to be redone to prevent leaks.

Roof-mounted hatches and air-con units can also be a source of water leaks in a composite RV, and eventually need a re-seal. Sometimes they can leak sooner, but that's usually the result of poor surface preparation before adding the sealant during the RV’s build.

Not all timber free

You might also find that a composite caravan isn’t all composite - many have a plywood floor, for example. That's fine if it’s marine plywood, which is waterproof – but if not the floor can be subject to rot or warping if there are leaks.

It also isn’t unusual to have an inner plywood wall in a composite RV. While ply is light, cheap and allows for more varied and intricate interior wall colour options, if the ply is damaged or gets saturated it can be very time-consuming and difficult to remove and replace as it's glued to the composite core.

Summing up, while there are many benefits of owning a quality-built caravan with full composite construction compared to the old-school timber and aluminium method, it doesn’t come without its own complications.