i had great success last year

i suspended a small sand filled terrarium in a 20 high aquarium

the inner unit was set on top of an inverted small flowerpot

i ran 2 aquarium heaters in the water that was even with the top of the sand in the inner terrarium.

one heater was set to 80,
and the other was set to 85 and on a 12 hr on, 12 hr off timer

the eggs were in a depression in the middle of the terrarium and covered with a damp paper towel

the thermal mass of sand was very stable in temperature and i could easily check on the eggs under the papertowel

a sheet of plexiglas acted as a cover over the aquarium

all the eggs hatched