Some people have had bad experiences with purchasing vehicles or someone told them about a bad experience they had or they have so little idea of what they buying they are scared. As a seller I avoid these folks, they are going to be a PIA. If I am a buyer, I would be equally reluctant to deal with someone who does not know about their rig.
1) If you don't know much about RVs and the seller does not either, then yes you should have it inspected. You might luck out and trip over a knowledgeable RV tech.
2) If you don't know much about RV's, but the seller knows about their RV, you may offend the seller by insisting on having it inspected. That would be me. You don't trust me, I don't want to do business with you.
3) If you know about RV's do the inspection yourself. It will take 3 or 4 hours to inspect all the RV systems, plus another two to test/inspect the Ford parts such as a/c, brakes, hoses, etc.
Most RV techs are worthless. Techs have little knowledge of RV's. So insisting on an inspection by an unqualified RV tech who the prospective buyer may not even know to tell them if the RV is as described might be insulting. There are three RV dealers in my little town, I would not let one of them touch my rig. So I sure would not seek their opinion on the condition of one.
If you are willing to risk your buying decision on the judgment of one person with known credentials, here may be the best way to locate an inspector.
I can tell after a few minutes of conversation if a buyer is overly apprehensive or the seller is trying to pull a fast one on me. If so, I avoid them. For instance, if someone asked me if the vehicle used much oil and I said that I had never added a drop. Then later they said they could not believe that it did not use oil considering the age and mileage. Well, they just accused me of lying. That would be the end of business for me.
You may think I am crazy, but truth and trust have always worked for me.