1. Get a copy of the HOA bylaws for the resort development. That will spell this out in detail. Usually, it's 10 years or management approval. So if your RV is a good condition there's usually no problem. At our summer place (Hearthside Grove) there's a number of older "classic" Prevost conversions. No issue with them, they're all well maintained. Our coach is almost 8 (model) years old, and I don't expect to have any issue with it for many years.
2. Not sure I understand the question. If you sell, you get what it's worth when you sell it. Might be more than you paid for it, especially if it's a popular resort and they're done building more lots. Or the opposite could be true. A well built and maintained casita should increase the value. But maybe not by as much as it cost you to build it.
Also, be sure that the resort allows for year-round, full-time residency. Some don't because of local zoning laws.
2008 King Aire 4562, Spartan K3(GT) w/ Cummins ISX 600
2014 Jeep Grand Cherokee Overland 5.7L V8 Hemi w/ Blue Ox Aventa LX Tow Bar and baseplate, SMI Air Force One brake