As a boater first I still look at RVs with a marine mind. For the most part RVs are not built to the standards I expect to see in any boat builder I'd be interested in. How some of them stay together as well as they do on the pot-holed highways is a miracle in itself.
Don't take the 30' max at many SP & NP CGs as gospel. Most have spaces that can accommodate larger however the larger you go the fewer the sites. We chose ours with SPs etc in mind. 11 years & hundreds of CGs later we have had very very few problems anywhere except CA SPs.
30' is small & for long term or full time you will get 2' itis very fast. We settled on our 34 because it has a larger than average galley, needed if you are going to full time & it goes everywhere we want to go. Interior space is about the same as a 38-low 40s trawler. The advantage of the RV is that if more space is wanted you simply step outside & go for a walk. Can't do that with a boat.