Hydrofarms and Johnsons controls a419 are both on/off thermostats and shouldn't be used for incubators IMO and from my experience
My 4 cubic foot mini fridge took 2 feet of flexwatt running along the back and heated it perfectly.
While I got a mini-fridge with the coolant removed already it's probably easier to leave the guts intact and just drill holes where you want the wires to run into the inc. that way you're not releasing it into the air.
I found that a fan is only needed if your using more than one shelf.
The thermostat probe can either hang in the middle of the inc or taped against the flexwatt, I had mine tucked in behind the flexwatt and taped so it couldn't move. That way the ambient air rushing in couldn't sway the t-stat very much.
The only readings your really concerned with is the temperature inside of the tub which you read with your probed thermometer.
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