Hi
I have a heat cable taped around 3/4´s of the underside of my tank...then I have a 40wt UV/heat bulb to simulate daylight over the top of the water tray. To
help keep the water warmer I have a small flat 15wt heater (it is very cold here in winter). I will turn this off as the days get warmer.
Goober often digs down but I have noticed he never does it near the heat cable, he tends to do it just to the side of the water tank,
he probably gets the heat from the moss from when the bulb was on.