If you have a uth giving a hotspot of 90 the entire cage can have an ambient temp range of 77-84. If you want a bit more heat retained you can even use thick art paper to cover three sides. I did that and I picked up a few degrees in my ambient temps.
I have a 40gal glass tank in a room that is a constant 68F. I have a uth, 100w che, and a 60w bulb to keep my temps within range.
The only issue I see is the amount of substrate over the uth. You should only have 1/4inch. Having that thick a layer makes is almost impossible for the heat to reach the surface for the snake. It also usually causes the temps at the glass to be very high. Where is the tstat probe?
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