OK,back to your original question. I've been using a C20 for the past 8 mos. and have been happy with it. One thing about though is the temp indicator is way off...like about 20 degrees. I use an infrared thermometer to periodically check the temp. A C20 is the same as a C15 except it has a larger top. It's still not high enough for a 1/2-gall. milk container though.
I've kept the usual fridge items in it: condiments,yogurt,cheese,lunchmeats,salsa,potato salad,milk,etc. With a 100w solar and 105ah battery setup, when there's several rainy/cloudy days in a row, the battery does get drawn down.
I was in a hurry when I set it all up last spring and don't have wiring/solenoid connected to my alternator but am adding that now along with relocating the fridge closer to the battery.
The C20 was protected in shipping by two pieces of foam at top and bottom and I used them plus some foam board insulation to better insulate. I built a little frame from scraps that holds a foam filter over the intake for the cooling fan.