A general tip from my experience on probes.. They do not need to read the tub temperature. Or enclosure temperature. You must try and find what works..

Ex
My probe is under my heat tape, grooved into the rack. And reads 103 deg at all times..

Tub Thickness, and heat loss throught the rack drops the 103 to 92 degrees inside the tub at the lay point. Substrate cools this further.

Regardless that its at 103, it stays there. So my inside tub temp stays constant all the tome. Thats what you want. Its some trial an error, but i do not reccomend putting the probe inside the tub, you run a big risk of the snake moving the probe.