Are you asking about paying someone rent to live on their boat? I think that is going to be a tough one. For one thing, due to the short season, people will want to use their boats in May after the long hard winter this year.
We stayed at the Manhasset Bay Marina once for a couple of days. It was a nice location right in town, walking distance to good supermarkets, restaurants and other shops. You could start by calling them and asking for advice.
There is a nice mooring field there, with tender/ water taxi service, which we have also used. Perhaps, I still think it is a very long shot, someone would be more inclined to having their boat looked after out there.
"There's the Right Way, the Wrong Way, and what some guy says he's gotten away with"