Do you really think that the temp of the outside of the radiant insulation would be anywhere near the temp of the surface of the flexwatt? Really man, use your head.
Think of how a forced air heating system works. Air passes over the heat exchanger in the plenum where it picks up heat and distributes it through your house.
Here the air is heated as it passes through the cavity in the door.
As to it being dangerous to have the probe in the fridge,...um you must be joking right. If the probe is not in there how would the herpstat know the temp? On the contrary, it would be very dangerous if the probe was not in the fridge.
I have had it running for a few days now temps are stable and even top to bottom.
People, whatever you do please make sure the probe is in the incubator with the eggs or you will cook them.