I bought a digital indoor/outdoor thermometer for $20. The small outdoor sensor/transmitter is very water resistant so I put that closest to the water bowl which is on the hot side. This measures the ambient temp well.


You can see both the main body and the outdoor sensor in this photo, both are inside the tank and run on AA batteries.

I did a boo boo though and didn't shop around enough to find one that measures humidity. I will buy one that can and use this one I bought as a regular room thermometer and outside thermometer.

I suggest saving for a similar thermometer. It sounds like you have a thermostat for the UTH which is great.