Ponding is water sitting on the roof when the 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 the very best but only appear on the 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 the side wall. I have never seen the 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 the drivers side and saw the fiberglass body delaminating. I didn't think it looked too expensive to repair. I figured caulk the seam and just screw the panel back tighter to the frame. Of course the salesman agreed.
WRONG! People do not realize especially in older coaches that the WOOD (yes I said the WOOD) that is under the fiberglass skin does offer quite a bit of the stability, and rigidity of the exterior. Once it gets wet for a prolonged period of time it rots, breaks down, and becomes heavy enough to cause the 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 the RV chat logs thus far).
Body integrity is one of the more important advantages that the big solidly constructed bus conversions have over 95% of the 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 the problem. Otherwise, I can assure you, it will destroy your experience and investment in a short time.
Mechanical Leaks - Look for ANY signs of leaks, particularly from Automatic Transmissions. Some Allison transmissions used in diesel motor homes have wimpy front seals and leak constantly when the transmission gets too hot. Don't buy an RV with a leaky transmission. A replacement Allison can cost $3,000 parts and labor to replace. Leaking brake components or hydraulic systems can be expensive to repair also.
Leaky radiators can be expensive to repair or replace on larger coaches especially if the labor to pull them involves pulling a lot of other items. Same goes for leaky dash air-conditioning systems.
Body Style - Check out the visibility differences. The entrance door positions vary as well. The rear pusher buses offer a quieter ride. Fifth Wheels usually do not have flat foors inside and almost universally offer the "split level".
Transmissions - Get an automatic unless you really like the absolute control of a standard and never intend to resell it. Standard shifts are MUCH harder to sell as conversions because retirees are the most common motor home buyers and they don't like to shift. Allison makes the best transmission systems in the world. Many older gas RV's were mated to inferior transmissions that just cannot handle the extra weight and pull issue.
Some RV's have engine/transmission setups that are so underpowered you will never be able to afford to use them. These transmissions are forever blowing seals, leaking, overheating, and breaking down. Buy a replacement transmission and guess what? Your only option may be a rebuilt version of the problematic transmission you already own.
Engine - If you are going to be traveling through mountainous areas regularly get the biggest engine you can afford. There is NO substitute for size (raw cubic inches) I don't care what the ads say. My car has a 440 in it. Why would you buy a 34' RV with a 318 in it? Check carefully how many miles on the engine or since the engine rebuild. Gas engines last about 60 -100,000 miles, depending on whether they are driven stop and go in the mountains or over long stretches of flat highway. Diesels can often approach 200,000 miles before needing much of anything with proper maintenance.
If economy is a major concern, look for a good affordable coach with a great miserly engine/transmission combination. I bought such a coach with a Cummins 190 HP 6 cylinder diesel engine mated to an Allison 4 speed automatic transmission. Over the course of our 31 day, 7,980 mile trip, in mixed traffic, tough mountain and city driving, we averaged 10.6 MPG in our 34 foot fully loaded class A liveaboard coach with 4 people and 2 kayaks.
NOTE: After evaluating the information above on SPECIFIC issues related to this particular platform you may find the prepurchase checklist found at http://busforsaleguide.com/bus_prepurchase_checklist.htm helpful. It covers GENERAL issues you should be aware of for ALL platforms. It will serve as a very valuable resource to assist you in evaluating a bus, motor home, or RV for purchase. Take a copy of it with you when shopping.
About the Author
Jason Odom wrote http://busforsaleguide.com as a complete website full of bus and Rv buying information including the advantages and disadvantages of each type, make and model. Jason Odom has 14 Years in the business of assisting people in finding the Bus or RV that meets their needs.