I used a coke machine and put (roughly) about 5' of 3 " heat tape in mine. I ran it from the one side, across the bottom and up the other side ( like a large U of heat tape) and set a simple on/off t-stat and it works great. I found that if you put a lot of the water bottles in there it helps the heat come back up faster when you open the door. I had great success with it too hatching out 3-4 clutches over the last 2 years. with a whopping 4 planned right now for this year.