Warning: I am not a tax professional or a lawyer. This is not legal advice. The value of advice from an internet board is worth what you paid for it. My wife says anyone who listens to me is an idiot...
I am a resident of Mass and have a boat in RI. It's possible to do what you plan but you have to be extremely careful or you will end up owing the tax anyways.
There's no problem registering a boat in RI as a Mass resident as long as it is moored in RI. During the first six months of
ownership, anytime spent in
Massachusetts (e.g. one night) means a sales/use tax is owed since there is then a presumption that you intended to use the boat in
Massachusetts when you purchased it. After six months, the burden is on the tax guys to show you had an intent to use it in Massachusetts when you bought the boat. They will enjoy doing this if you are stupid enough to leave some sort of paper trail that indicates this was the plan all along.
Since I don't enjoy any discussions with tax guys, I didn't cross into Massachusetts waters for over a year.
The second tax is the town property tax. This is paid to the Massachusetts town where the boat is "habitually moored". I'm not sure what this means but if you decide to have a seasonal slip or a
mooring in Massachusetts, you will pay this tax. Luckily it's not much. My guess is that for your boat it will be about $300 a year.
I know even less about
Florida so I won't even try.
Carl