FWIW, there's not "a lot to rot" within our 2005 Itasca's walls as far as I can see.
Only just steel and aluminum struts and beams and white foam insulation are actually inside our Itasca's walls. Most of the wood is in the interior of the coach making up cabinetry - not contained with anything else that is hidden and can rot. The inside and outside wall material itself is not a wood product, either.
Of course one of the most insidius places for leaks to form in some Class C motorhomes is along the roof's long side edges. In at least our Itasca, both of the long roof side-edges are molded rolled-over edges of about 3 inches from the single piece fiberglass roof itself. So unless water can run uphill, these edges aren't going to leak.
Maybe some mold can form in wall interiors from leaks - but no structure rot.
If some of you Itasca owners from the 2000's onward know of interior wood ... please let us know where it is.