I just heard of a product called GoBoard - it's primarily meant as a backer board for tiling, but I'm thinking it might make sense to use just kinda everywhere in a bus.
Quick summary of advantages are:
- It's intrinsically waterproof (fill seams with proprietary caulking and you're water tight)
- Extremely lightweight
- Easy install
I'm also suspect that there might be some insulation properties to it. It sounds like it's
sorta-kinda similar to that extruded foam board stuff; meaning it sounds like it's an aerated plastic board. But that's just a hunch.
Curious to hear from someone that knows better. My thinking is that it might make sense to use it everywhere in a bus. Waterproof (thus a moisture/convection barrier too), lightweight, simple install, and (maybe) some R-Value to it.
You could always put something prettier overtop of it.