It would not make sense to put the probe right on the heat tape as my tubs do not come into direct contact with the tape... and the ball pythons do not interfere with the probe as it is glued to the wall of the tub. Because of there being no space on the bottom of the tubs, I cannot put the heat tape on the bottom. The tubs are tight as it is. I took the back off of the rack and I think I figured out the problem. The bottom part of the heat tape was crunched and was providing no heat. I put new heat tape down and so far so good but they are still warming up so I will see in the next few minutes.