Need help with my first tub Setup

[Vypyrz]

I would go ahead and mount the probe on the outside, between the heater and tub, and reduce the thickness of your substrate to about 1/2 an inch. That should let the heat dissipate better, and not build up under the substrate. I would suggest a temp gun, instead of a heat gun.

[Reptile Frenzy]

I meant temp gun...