Organizing a pre-sale inspection...
You need to discuss with the dealer your need for an independent inspection (at your expense, of course). Some may not be cooperative at all, perhaps claiming it's not needed because they "inspect everything" themselves. I would advise walking away from those. If they insist on a sale contract before allowing an inspector onsite, definitely have the agreement stipulate that the sale is contingent on your satisfaction with the inspection report. Not just a "good inspection" or similar words - YOU are the only one who must be satisfied and it is soley up to you to cancel or proceed. And make sure any deposit is 100% refundable if you decline.
Do not assume that buying an RV at a dealership is like car-shopping at a dealer. In some ways it's similar to buying at a used car lot (and RV dealer ethics are often much like the proverbial used car sales guy) , but the whole process is more analogous to buying a furnished house. The condition of the roof, appliances, plumbing and electric systems are all as much or more important than any vehicle concerns.
You should assume an inspection will find some problems, or at least some items that need attention. After all, it's not a new house/vehicle. Whether any of them will be show stoppers is a more difficult problem. You should also be prepared to negotiate with the dealer on any items the inspector reports, either asking that the item be repaired or replaced, or accepting an additional discount in lieu of repair, or even just taking the item "as is" and getting your own repair later.
There are RV buyer Checklists in the RVForum Library - a whole section devoted to them in fact. A couple of the lists are very comprehensive, but do not assume that every inspector will do all the items. Discuss with the inspector what he will actually do, i.e. does he just "eyeball" on item for working condition or does he actually test & verify. For example, will he actually operate the fridge long enough to see if it gets to operating temperature, or does he just turn it on to see if it begins to run & cool? Are the batteries tested under load, or does he just turn the lights on to see if they light up? You get the idea...
http://www.rvforum.net/joomla/index.php/15-checklists