Why all manufacturers do not use composite?

Azdel is a composite, and we're glad we have it in our Aliner. Our camper developed a leak in a driving rain storm because the running lights on the front had not been caulked properly at the factory, and we incurred no structural damage because the camper has composite sides/floors/roof. The only damage was to the wood frame of one dinette side where it touched the floor, which was easily replaced. We shudder to think how much damage there would have been on a stick built camper.

I believe that the Coachmen Apex uses a composite, at least on the roof, but I'm not sure about the walls/floor.