There are a few manufacturers out there. Marine Air is probably the most common. Webasto also makes popular units.
https://www.defender.com/category.js...077&id=2061083
You'd be looking for a 6,000 BTU unit.
You'll need to install a through hull with a seacock, a seastrainer, a continuous duty circulation pump, the hoses leading to the systems, discharge hose and a discharge thorughhull. Then the ducting through the boat.
I think they installed the unit behind the fridge.