Not that many people live on boats where winter is a serious event (e.g. where the water
is too cold to do reverse cycle A/C) so there aren't that many experienced installers. This will take patience.
First. What kind of heat? Diesel
(Espar is the most popular). Or electric
resistance if your marina has good electric
service. Or some of both?
For Espar, I've used Ocean Options in Tiverton, RI. They have a lot of experience and travel (although I don't know how far).
I would think about getting advice from other liveaboards at your planned winter marina as to what approach to heating works best (cost, reliability
, service availability, safety
, etc.). Be sure you have a way to get the system fixed quickly if it breaks in the middle of winter. These systems are not nearly as reliable as a heating system in a home.