[[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 is running.