RV vs Boat?
Well the differences are kind of the same. I'd suggest attending some boat shows and seeing the sizes/space and deciding on what you think will work for you.
Take some boating classes, The coast guard aux classes will help. You have to learn the rules of the road and navigation. Sailing classes if sailing is what you decide on.
If you are in a RV now than you probably pay for a camp site, it's the same for boats at marinas. There are some sites that list marina prices. They can very wildly. Of coarse you can never tie up and stay on the hook too.
The biggest problem we have found by talking to many live-aboards is transportation at each place you stop. You are limited by taxis, public or renting cars to get around. You might find that hard to get used to coming from a RV where you can drive where you want. But than again on a boat you can get to places others can't.
Just somethings to think about.....