Originally Posted by panheaddale
Coosa products are a little pricey compared to plywood but if you are restoring a vintage camper and don't want any rot issues ever this is the way to go. They have a product call bluewater 26 that is structural quality. You will save about 100lbs on weight compared to plywood for a 26ft trailer. Cost is about triple what plywood is but NO ROT ISSUES EVER.You don't have to spend hours sealing and still wondering when you wood is going to get wet and rot.What is that worth? Coosa Composites, LLC - Manufacture of high-density, fiberglass-reinforced polyurethane foam panels
Yes a bit pricey, but if you're going to do this epic job you might as well do it right. You can save a bit by running with marine ply in the middle of the trailer.
I used 3/4" Bluewater 20 as a marine place told me that spans of 16" or less were just fine for the 20. It was very easy to machine down to the thickness of the C channel and was very difficult to break. Since I went with the 3/4" instead of 5/8", any water coming down to the C channel would stay there and drain out of small 1/8" holes I drilled through the channel, as water doesn't run upstream.
If I were to buy a new Airstream trailer, I would deliver however many sheets of Coosa right to the factory to build my trailer, just MHO.