Through the years, I have found that the best systems for my use are the holding plate systems. The problem with most boat refrigeration systems is that the boxes are not properly designed or made. The insulation needs to be fully closed cell--for a freezer at least 6" and for a refrigeration, at least 3". There needs to be a reflective barrier and vapor barrier on the outside and inside of the box. The doors need to have a double gasket and compressive locking handles (like the old ice boxes). We used dual systems, with off the shelf components--the engine system used a Sanyo compressor and the 110 volt system used a sealed compressor--with both air and water cooling. At a dock, the compressor was on a timer (but it could be on a thermostat). We kept the freezer range from 0 F to 10 F--and it was very adequate to keep products frozen for months. Both the freezer and refrigerator were 12 cubic feet, and my wife made frozen food for all of our passages. Often she would cook enough food for 3 months, freeze it and store in "seal a meal" bags. One could run a compressor off an inverter and large battery bank, if necessary when one left the boat at anchor. But we rarely left the boat at anchor, without someone aboard if we left the boat. On our trawler, where we had a household refrigerator, we used two 12 volt computer fans for cooling the coils. The fans were on simple household thermostats, and only came on when the temp around the coils went up above a set level.