Recreational Vehicle Buyers GuideService Records - If you're buying from an RV dealer and they can't produce something - you've got problems - possibly serious ones. If not, he'd be proudly displaying records. There should at least be receipts for repairs, service work, and possibly old owners manuals.
See http://busforsaleguide.com/rv_types.htm for advantages and disadvantages of each major class of recreational vehicle on market.
Body Leaks -Other than structural rust, I know of no other exterior related problem that will cost you as much money and cause you as many headaches as exterior body leaks. Body leaks are among most difficult to fix if body design is less than first rate. Front facing windows on many Class C's are nearly impossible to stop leaking due to flexing and stress.
I have been incredibly pleased with purchase of my 1993 Class A. However, wood over skeleton frame roofs like type Georgie Boy used in this coach has begun to sag between support tubes or "skeleton". The weight of air-conditioners, vents, my roof mounted kayaks, and walking up there to fix seams, has permanently created "ponding" issues. Price quote from my very trusted and competent local RV service center was $4,200 to rebuild my entire roof.
Ponding is water sitting on roof when coach is level. When this happens you have increased chances of leaks, bugs, slime and algae growth, and dirty water run off when you drive somewhere. Rounded formed fiberglass roofs are very best but only appear on newer coaches that were out of my price range.
I have seen $30,000 to $60,000 coaches nearly ruined by leaks that went unchecked. Be especially cautious if you see ANY delamination of side wall. I have never seen permanent damage fixed for less than $4,000 and that is WITHOUT a guarantee that it won't happen again. This is usually caused by poor roof and seam design.
Nearly everyone underestimates how serious this is. I know I almost bought one. Couldn't figure out why a great looking Santara diesel pusher would only cost $24,000. Then I walked around to drivers side and saw fiberglass body delaminating. I didn't think it looked too expensive to repair. I figured caulk seam and just screw panel back tighter to frame. Of course salesman agreed.
WRONG! People do not realize especially in older coaches that WOOD (yes I said WOOD) that is under fiberglass skin does offer quite a bit of stability, and rigidity of exterior. Once it gets wet for a prolonged period of time it rots, breaks down, and becomes heavy enough to cause entire skeleton to sag. Windows no longer fit right, seams pop open worse, storage doors underneath stick, and on and on. Do NOT buy an RV with this problem. It can cost as much as $13,000 to fix (highest horror story I have read about on RV chat logs thus far).
Body integrity is one of more important advantages that big solidly constructed bus conversions have over 95% of factory built RV's in use. Do NOT purchase an RV that has signs of leaking without a thorough plan for paying for and fixing problem. Otherwise, I can assure you, it will destroy your experience and investment in a short time.