Windows in RVs should be removed and resealed every few years as routine. Most leaks come from the roof, some windows, some drains for AC, etc.

Using an unvented propane heater in an RV will cause condensation damage. As bad as a leak.

If the wood is bad enough that you feel like it needs to be coated, it needs to be replaced.

Kerry is right about the metal frame. A paramedic buddy says that the metal frame might not save you in an accident but at least they can identify your body. Same with a motorcycle helmet.

Flat roofed RVs are not something I would own. Some of the plastic roofs were problematic too, search by make and model for stories.

I might buy another RV soon. Maybe a 5th wheel with slides. I also always liked the Wanderlodges like Kerry is referring to and has listed in his sig.