I use a "reptile heater" to provide the heat needed. It is basically a low wattage heating pad that is intended to be adhered to the bottom of a reptile tank. The first one I got was 7W, but for the bigger chest freezer I've got now I got a larger 16W one. When it is "cold" out in the garage, I just put the heating pad in the chest freezer and leave it plugged in. I have the A419 temp controller. It will run the freezer and the temperature will undershoot the setpoint by a couple of degrees, the heating pad will slowly bring the temp back up until the controller turns on the freezer again. I admit a dual stage controller would probably be better, but this is working fine. There are higher wattage (60W or 100W) ceramic bulb style heating elements, drawback to those is that they aren't supposed to get wet.