The ceiling and wall boards in my weekender have water stains on them from leaks - lots of them.  I've fixed the leaks, but now need to deal with interior damage.  I was going to paint the walls and ceiling, but have decided against doing this because I think it would be a royal PITA and I'm not sure what the longevity of it would be.  What I'm now thinking of doing is replacing the boards.

Where do I get the boards?  I don't know where previous owner (who finished weekender himself) got them.  Ceiling is a flat, smooth, glossy white.  Walls look like wallpaper.  Believe it is RV wall board.  Can the backside of the boards be waterproofed so that any potential, future leaks don't leave a stain?  Also thought about caulking the roof seam on the INSIDE since I will have access.  This would be backup protection should my exterior caulk develop a leak.  Has anyone done this?  Pros/cons?