Thermometer ALWAYS goes inside. The thermostat PROBE NEVER goes inside. All it takes is one massive poop or pee on the probe and it will cool the probe down. Then this will cause a spike in the UTH thus BRUNS.
Always ALWAYS keep the thermostat probe OUTSIDE secured onto the UTH directly with tape or hot glue. The UTH will heat the glass and substrate to the set temps in 1-2 hours no problems.
I'm sorry, I was only talking about the thermometer. Not the Thermostat. I agree, thermostat probe goes outside. I should have clarified more. I misread the other post.