I used to tape the thermostat probe inside the tank directly to the bottom and I've been scolded by numerous users on here for doing that. The problem is that the warmth will allow the tape to come up easier and if it gets attached to your snake's skin, it can rip the skin off. The other issue (which you won't have since you're using a rheostat) is that if the snake pees or tips the water bowl, it will cause the temps to be read lower. If you're using a thermostat, it will kick the UTH On and potentially burn your snake. Tape the probe to the bottom of the UTH with some heat insulation tape and you can achieve the same thing without risking your snake's well-being.