Strength, UV resistance, light weight, good insulation properties, easy and quick to work with and reasonably priced are the attributes one wants from body material, but such a thing does not exists. One can find a multitude of composite panels, which meet most criteria but are definitely not reasonably priced for the home builder.
Steel frames and aluminium cladding are still very common amongst caravans. The reason is most likely material cost, however any frame construction has an enormous labour component, where in comparison a composite panel should compare favourably. For a home builder like me the labour side is not as cost critical, however the weight of a steel frame in the intended length of the van is not really a motivator for that very traditional concept.
Meranti or aluminium frames are just as laborious and have other downsides. Generally the frame built vans have cladding and for one this looks outdated and also is harder to keep water proof. Stress cracks and separating panels are common, rot, corrosion and broken frames are not unusual. As a home builder with little manufacturing experience one may fall into a bunch of traps using such a technique.
I have been thinking about using FRP extrusions as a frame, which has many advantages and skinning it with FRP/gel coat skin, insulating it with polyurethane foam and skinning the inside with ply wood panels. I made complete designs in my CAD system. This would be much safer to build as far as leakage is concerned, because one can make sure from the inside before the insulation goes in that all corners and joints are reglassed and completely sealed. This method is cost effective and not more expensive than any of the other frame techniques, however bonding a sidewall of 10.5m length to a frame is not an easy job either.
Another disadvantage of cladding is that you do not get a flat surface to mount windows and baggage doors easily. With the number of doors and windows I have to fit this seemed like a daunting task. Denting is another downside of cladding and especially with storage all around and below the floor the possibility of stone damage and denting is real unless one uses tread plate as many do, but that adds another weight factor.
At the end of the day it all boiled down to weight, simple as that. A composite panel is more expensive but lighter, stronger, better insulation (most of them – not honeycomb panels though), all openings can be cnc precision cut, and in total it is quicker to be put together. While frame vans have a lot of cables inside the walls this is not easy or possible with composite panels. One has to find other ways for routing the cables but if done right this leads to better accessibility and repair if required.
Not all panels are suitable for all purposes. A floor panel should be strong and have a good span with little support underneath. Honeycomb panels fit the bill as far as strength is concerned. There are different variations on the market, some use fibre glass and some use an aluminium honeycomb. Depending on thickness they are suitable for structural applications. The downside of a honeycomb panel is the lack of insulation properties. One could think that this is not that important for the floor, but it is. A plywood floor is heavy and a bad insulator, but the standard in Australian van building. One can never achieve a class III insulation with Plywood. I always have a bit of a laugh when I read the sticker “fully insulated” on a caravan wall and it has a plywood floor. Very few go camping in sub zero temperatures I guess but even in 35 degrees heat a well insulated floor will keep the inside cooler. Granted that the body is more important as far as heat transfer is concerned, but still the floor does have its contributions to heat build up. We intend to go into the snow and want a good all round insulation, but I come to that later in another chapter.
At this stage I have not made the final decision regarding floor material. The body will be a composite panel, that is clear so far, but the supplier I deal with is also currently looking at another foam material and we might be able to even further reduce the weight. But this has not yet been decided.
The floor in the neck area does not require the same insulation properties as the main floor and I will do it with Venturelite 2020, an aluminium honeycomb core with aluminium skin.