Connect incubator fan to thermostat?

I built my incubator from an old upright freezer, with Flexwatt wired up to wrap around the middle section. Does my fan need to be all the way at the top of the incubator, or just above the heat tape? Should I run the fan through the thermostat, or have it plugged in to run at all times?

Thank you!

For my fridge I put the fan at the top of the incubator and let it run all the time so they temps stay even throughout as much as possible at all times.