Thermostat / Multi-Tub Rack / Temp Variation

[JohnNJ]

I am trying to grasp the concept of using a thermostat with one probe to regulate the temps in mutiple tubs in a rack. From what I've read, the tubs at the bottom of the rack are cooler because they're near the floor. The tubs at the top are warmer because heat rises.

Where do you put the probe on a multi-level rack with belly heat?

How much temp variation is there in the tubs at top, middle and bottom?

How is all of this affected when the rack sits in a room where the temps fluctuate 5 to 10 degrees, plus or minus?

Thanks.
JohnNJ