Something I have seen done on some alt energey web sites/forumsis to take a small top opening freezer and disasseble the thermostat and replace it with a refirgerator thermostat. Freezers have a lot better insulation than refrigerators so that cuts down on run time, the door on the top also helps prevent the cold air from "spilling" and they have better compressors. SO by switching to a refrigerator thermostat the compressor has to run fewer cycles to maintain the less cold that what it was originally designed for making a very efficient refirgerator.
There are also high quality 12v refirigerators, not the cheap crap in the rv stores but the expedition quality stuff. Downside is they cost about as much as a regular refrigerator for a cooler sized space. But if say you have someone that needs medication such as insulin to live then cost isn't as much as a factor. There is a forum called expedition portal where I found some brands and info on those.