Like they said above, anytime you make a change to their enclosure, it takes a few days for the snake to re-adjust to their new surroundings.
Something else you can cover the screen with is aluminum foil. Just leave a hole for the lamp.
When you get the UTH, you will also need a way to control it. An unregulated UTH can get way too hot. A digital thermostat is the easiest way to do this. You can order a good basic thermostat for about $25-$30 here:
http://www.amazon.com/Hydrofarm-MTPR...1529683&sr=1-7
Another option for controlling a UTH is to use a simple lamp dimmer switch. You can pick one up for about $10 at places like Lowe's or Home Depot in the lighting section. Here is a link to a thread with some photos of what they look like:
http://ball-pythons.net/forums/showt...t-Instructions
Hope this helps...