I am working on recycling an old fridge into a bator. What are your suggestions for a thermostat would rather not use a wafer system unless I get alot of rave reveiws. I have ordered two thermostats off of ebay same kind but they wont hold temp in a large styrofoam cooler they are ranging between 107 and 90 without touching them. Here is a pic of what they look like. Any suggestions?