Full details are here: http://2manytoyz.com/engel-thermostat.html

The Engel fridge is great for camping, traveling, or for when the grid goes down. The issue is the fridge came with a dial, with settings of 1-5. That thermostat works on a temperature Delta. If the ambient temp changes, so does the inside of the fridge. Using readily available and inexpensive parts, I built a digital thermostat that's external, and requires no modifications to the fridge itself. The remix of this case was to make it large enough to fit all the components.