Wow. As someone who has done mechanical inspection on motorhomes for a number of years, there are what I find to be some very "interesting" responses.
Let's divide the components into the various categories-- some of which you may be able to do yourself, some you may need outside help for.
With a trailer (assuming you are good with preventive maintenance and know how and what to check) you can likely check the house systems yourself.
Chassis-- that is where most RV inspections fall apart. If diesel, did they check the SCA of the coolant? check hose routings for chafe, help you determine what needs to be done from a Preventive Maintenance perspective and help you decide what you want to tackle and what needs to be hired out. Rust? Brakes?
Body-- I start on the roof and end up under the coach. You are looking for evidence of water leaks, delam, gel coat cracking, signs of damage.
Ya, this is only a partial list.
Unless I am very familiar with the item, I would NEVER buy something without an independent inspection-- I have been that way of each of our boats, houses, and our first motorhome. Cheapest money you will ever spend.