We have an Engel brand refrigerater/freezer that runs on 12 volt
or 110 AC that is wonderful. But, it is expensive, around $700. It has a control that allows you to set the temperature that you want. We have used it in freezer mode to bring back shrimp and fish from Florida to Colorado over a period of several days, and they remained frozen solid for the entire time. It is roughly the size of a 48 quart ice chest. ARB is another brand that is very similar. These refrigerators are made in Australia and are used extensively in the outback there.