Unless you are military or diplomatic, there will be import issues (duties or bonds inlieu of) and even vehicles taken over per armed forces treaties have to be modified to EU safety standards, mostly lighting issues. The RV stuff like LPG fittings and power is different, but you could always modify, replacing components with Euro standard, or adapt.
Going over as a tourist, bringing your own vehicle, is a different regulatory regime, more flexible, than being there as a resident.
My limited experience, Spain, Italy, France, Germany, Austria, full hookup RV parks are rare, RVs in campgrounds are largely dry camping. Typical campgrounds I've seem have been fields on flood plains, where the land does not work well for more valuable uses.
Going over for three years, my inclination would be to buy there if I was using the RV a lot, rent if using one occasionally. You could be looking 5000 to 15000 Euros for something in the '90s, maybe 25,000-30,000 under 10 years old, 40-60K new depending on how big and how fancy.
Market values for used American RVs, especially those converted, are pretty high, they are rare and considered luxurious. Thus duties may be based on local market value rather than value in U.S.
29 foot is not small. 7 meters is typical for the RV camping environment, 9-10 meters of length is relatively large and combined with 8 foot width may limit mobility, or at least parking availability.