Ok, here's the thing with glass tanks:

1 - You can't use lamps any closer than 8" or you'll lose your humidity. Lamps should only be used for ambient temp boosts and viewing.

2 - You must cover the back and both sides of the tank with opaque background (for snake security) and some form of insulation. Foam board does quite well for this.

3 - You MUST cover the screen top with either fitted plexiglass or the foil treatment (3 layers shiny side down) to keep humidity and temps stable. Very few other materials work, and you absolutely should not use cardboard (soaks all the moisture into itself) or towels (breeding ground for bacteria when wet and also soaks the moisture up).

If you do these basic things, as well as have a UTH on a thermostat to control heat output properly and a good digital thermometer and hygrometer to get accurate readings, then tanks work just as well (if not better for some) than tubs.

I have a tutorial on how to set up the foil treatment on screen tops if you'd like me to PM it to you.

I use Aspen in all my enclosures, tank and tub alike, and it's the best snake bedding next to plain newsprint paper (which is boring and best for QT or having many snakes). It holds the humidity quite well. You issue may also come from following the bag directions (which are always outdated). For snakes, and especially Ball pythons, you only need about 1/2-1" deep. Just cover the bottom and not much more.