First, you need to read this caresheet carefully and fully:
http://ball-pythons.net/forums/showt...s%29-Caresheet
Under the substrate part it recommends:
Just find which of those suit what you're looking for. Coconut husk-based might work, repti-bark, aspen, cypress mulch would probably be the most natural looking, but its whatever you think looks the best. I can't say anything about the cat litter. I personally use paper towels due to the ease of cleaning it--I know I wouldn't clean the cage nearly enough if I used one of those."Some viable options for substrate include but are not limited to:
Repti-Bark or Jungle Bark type chips
Aspen
Newspapers/Newsprint
Paper towels
Carpet (harder to maintain)
Cypress Mulch
Coconut Husk-based substrates
Care-Fresh or similar products that do not pose impaction risks"
You should cover a majority of the top with something more than just a towel--it will keep the humidity in better. Just leave enough open to allow air to exchange.
I would recommend buying a thermostat before connecting the UTH, and an accurite thermometer/humidity reader to tell you if you have the hot spot and ambient temperatures correct. You might want a dimmer switch too for the heat lamp to get the ambient temperature correct. Or, if you don't need it, just the UTH without the bulbs would help maintain humidity.