There are too many chances for failure if you put the probe inside the enclosure. It could get moved, defecated on, wet, etc. Which would give your thermostat an inaccurate reading, meaning it could keep pumping power to the UTH even though the temp is where it should be. Then you end up with a cooked snake

To set up your thermostat temps, you need to have a thermometer and or temp gun to check enclosure temps. For example, I have my hydrofarm set to 94, the glass reading under the substrate is 91, and inside hide is 89-90. Temp guns are awesome