Set a temperature, have an exhaust, the temperature inside will be within a wibble of your set-point because the air stream will completely dominate over any other source of temperature raise/drop. You're way overcomplicating things. Forego subtlety, consider the air as a bulldozer: If this was a closed system having feedback control would be a good idea but air frying is supposed to use fresh outside air so that the hot air is really dry and the intake air being a couple degrees hotter or colder won't make a difference in practice. Just smash that shit.