Ok, here's what you need to do:

1 - cover the back and both sides with some sort of background (for looks) then with foam insulation board. Glass does NOT hold heat on its own and needs help. This will keep the heat IN the tank.

2 - wet towels breed bacteria. For the screen top, treat with foil or plexiglass for optimum heat and humidity retention. I have a picture tutorial up in the caging forum on foil treating a screen top.

3 - change substrate to aspen. That Reptibark stuff molds and isn't too comfortable for the snake.

4 - you already know it, but you need two identical hides that are all-surrounding with one opening. Plastic plant pots and plastic bowls from Dollar Stores are great and cheap.

5 - you might want to add more plants or decor of some type to make the snake feel more secure.

These are all suggestions, of course, but they should help a lot in stabilizing your tank.