Several heat lamps aren't necessary. I've got a UTH covering half the length of a 20 gallon tank, and the sides insulated with foam core. I've got the top 2/3 of the screen lid covered in aluminum foil pasted to firm card board. I have consistent temps and humidity and only use my space heater for cold nights to bump up the temp a few degrees. If you keep the sides of your tank insulated, your ambient temps inside the tank should be much warmer than in your room.
This might help: http://www.ball-pythons.net/forums/s...d.php?t=78239&