I added a eutectic holding plate to an existing icebox
in 1993. I did not modify the box, so it is still an icebox
, if needed. I installed myself a Technautics holding plate to the ceiling of the box. I got the largest plate. Technautics is designed for diy. You will want the largest plate and compressor
you can have. It pulls the box down to 23F and makes beer
slushy. Put the stuff you want to freeze right next to the plate. IMO you cannot make hot or cold with batteries, they will run down fast. You need to run the gen twice a day, at breakfast, and dinner, for an hour or so, to pull down the plate. You should have from 3" to 8" of insulation
around the box.