The key to longevity is maintenance and staying with the seals and caulk. I check mine every 3 months without fail and go over every inch. Especially where the water pressure is positive, on the nose and underside of the cab over plus any forward facing seal lips on vents or any items sticking out from the side panel like water heater vents or fresh water fill ports.
On the composite wood thing...
I was going to build a wood mat for the pan in my wet bath from composite but after I compared the actual weight of the composite against teak, teak won out hands down. The composite material was almost twice as heavy.