[[Full disclosure: I am the owner of Technautics CoolBlue Refrigeration.
Regardless of the type of system, making sure the box is properly insulated will be your most important task. We have installed cold plate systems in several cockpit
boxes, the latest being a SeaWind
Cat. If you don't have at least 3" of quality insulation
maintainig the freezer temps to properly freeze fish
and keep ice cream frozen will be a challange from an energy usge standpoint.
You mention your boat is 220v, but I would recommend looking at a 12v DC system that can run from your batter bank rather than something that can only run while the generator