IMHO opinion water intrusion and / or delamination has more to do with the area the RV is kept in, the amount and type of maintenance, or lack thereof, it receives, more than the type or style of construction.
A friend of mine bought a 15 year old Class C motorhome from a retired farmer, the only time it wasn't parked inside an equipment shed was when it was rolling down the highway. It is in perfect condition.
He met the owner of the exact same year, make and model unit at a rest stop on the highway. The other owner was amazed. His unit was badly delaminated and the cab-over bunk was in need of some rot repair.
