I installed a 110v Haier undercounter fridge and run it from an inverter underway and anchor. At the dock I move the plug to the shore power 110v. It's been running that way since 2000. It's well vented and I always meant to add power ventilation but have not yet gotten to it.
If you go with an undercounter unit, find one with a real separate condenser coil mounted in back. Some of the newer ones have the condenser coils molded into the sides. It's easier to vent them out the back.
The unit was $99.00 in 2000. Biggest problem installing it was getting the old Dometic unit out the door. Screws hold it in place covered by new trim. The door was reversed to make it easier to open in the galley. A barrel lock keeps the door closed underway and props it open during the off season. I always meant to paint the door brown but you know....
34' Marine Trader