I haven't tried but the idea looks great, and these guys explain in detail all you have to do, which is not much.
In broad lines:
Take a chest freezer (the lid is on the top, when you open the fridge the loss of cold is way lesser than a vertical one; the insulation is better than for a fridge).
Bypass the freezer thermostat using a new one to allow cutting off the energy when the temperature is reached.
A little more and you've got it.
Check the original site:
http://mtbest.net/chest_fridge.html
The original post is there since 2004, but I haven't seen any ref. to it elsewhere.