I suggest you contact DMV to find out what is required for a new resident to get an enhanced driver's license, or what ever RI calls it. Also voter registration. And a bank account. And a billing address for insurance or something like that.
I've thrice since the formation of the department of homeland security been through establishing residency in a new location without home ownership or rental lease and getting mail through a post office.
First time I used my adult daughter's address.
Second time I use a private mail box, they allowed me to use their street address as my residential mail address. That allowed me to get bank acts etc. That made me a resident in the eyes of officials.
Last time I managed to get a voter registration online, then got an enhanced driver's license. The rest fell into place.
If your chosen marina will let you receive mail at their address and claim it as a residential mail address that will ease things.
Some will depend upon how automated RI's systems are. If it's mostly manual entry and things look OK you may not have too much trouble. If they use an automated system that flags business addresses as non residential you may run into problems.
Start early, be patient. Don't argue with the clerk in front of you try again another day or another office.
One thing I found that seems to help is to use a rural office. The clerks there seem to be more willing to help than urban clerks.
I've lived aboard off and on since the 70s. It used to be simple. But now it gets more challenging to establish myself each time as security gets tighter and tighter.