One main problem with putting that probe inside the tub and under the substrate. ..... If your snake moves it out of the way(as they will) guess what, is cooking time and that thermostats gonna sense the cooler air and crank it up to full power and won't ever get the reading is looking for. I used to do the same as putting it under the substrate, luckily I changed my method before any snakes were harmed. Just a thought =)