I did a hot water heater thermostat mod as shown in the link below and could not believe how steady the temps stayed. I used a light bulb for heat and the temp swings were always 2-3 degrees before doing the mod. After the mod the temps were within a half degree. Try it you'll like it.
I get the same results by putting the back of the thermostat around 3 inches from the heat source as in this page http://cmfarm.us/WHTincubator.html
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