reptilebasics heat tape issues

[Mojo9120]

hey everyone, i just finished setting up two 3'Lx2'Wx1'H reptile basics PVC cages, i also purchesed the heat tape they offer to fit the bottom of the cages.

i set the thermostat probe floating to read the ambient air temp, it was saying that it was about 75° so i felt where the heat tape was and it was extremely hot, i set the probe on it and the temp shot up to 163°(way to hot for my hognose's) now i have the thermostat probe sitting on the bottom of the tank where the heat tape is, i have it set for 90° but the air temp is sitting at 65-70°.

my question is how can i heat the cage without dropping another $200 on two RHP and without drilling into them...