We love are isotherm, it will keep chicken frozen for weeks if it's up against the cold plate. My box has 4 to 6 in of fome and a tight seal on the lid. My isotherm uses a heat exchanger through the sink sink through hull. It use very little juice, but I'm sailing in Maine and the water temp never gets much over 62F. It also makes no noise.
Our Isotherm salt water cooled 12v fridge has been running continuously for 8 years with help from solar panels, and mostly in a sub-tropical environoment where the water is relatively warm. Exceptionally quiet and looks after itself. We love it. Works best with plenty of insulation.
We installed an Isotherm sea water cooled unit a few months ago - so far so good. We bought the 4203, which may be a discontinued model, as Isotherm was selling it on eBay. It is a holding plate system, medium sized plate, but the plate is cooled down to 0f, not 14 or 16 as usual with fridge systems. It is made to be a Freezer. The installation is as a spillover fridge, and other than coming to grips that we will need to rebuild our icebox, we have been happy with it so far.