If you are building your own box put as much insulation around it as possible. This will reduce the power consumption. On my previous boat I had 50 mm of polyurethane foam. This was OK but on my new boat I am increasing this to 150mm with through hull condenser. Previous boat has internal heat exchanger with pumped sea water. Seawater pump was the noisyest part of system. As far as I know all kits use the danfoss compressor.