There's one common thing that happens to RV's that sends more of them to the scrap yard than the next 10 reasons combined - 2 words - water damage.
Learn what it looks like in all it's different forms, where to look for it, and move on to the next coach when you find it.
If you find a coach with no water damage, THEN you can get serious about having it checked out/tested.
1997 37' HR Endeavor, 275hp Cat, Freightliner
03 CR-V Blue Ox, Ready Brake