Many places where you can fly and rent an RV by the week and see if it is what you want. Advantage in flying is that most of your time is spent traveling around a scenic area and not driving across the country. After renting one or two RV's you will also know a lot more firsthand about what you want in an "RV" whether it be a Class A, B, C, or a travel trailer.
Boats are more limiting unless you leave in the southeast part of the USA where there is the inland waterway and lots of lakes and other areas to boat-camp. Important to also know your limitations and match the boat to your capabilities and lack of experience. Boat weight goes up disproportionately to the length and the heavier the boat the more than can go wrong and the greater the chance of injury for a novice. There are Power Squadron and Coast Guard Auxilary classes that are a great place to start your education.
Mistakes with either an RV or a boat purchase can be very costly and advice on forums is not going to take you very far. Need to get your toes into the water and learn through direct experience.