I actually worked for a company that did van interiors ... I did the murals and paint work ... ended up doing about 8 vans for myself over time ... used fabric and carpet in abundance , and never a problem , even in our "killer" Humidity ... all were vented .... and waterproof ...."camping" trips were FUN !!! Vans were great for all sorts of spontaneous activies .... Ahhhhh!!! the 60's and 70's
Fabric was stapled/glued over a 1/2" foam padding onto a piece of thin ply or cheap paneling ... panel then screwed to ribs..many wild variations possible ... panels easily changed if damaged ...