FIRST: The MAX high temp for your hot spot should be no higher than 95 degrees. Your terrarium is too hot. 88-92 is generally recommended.

You can use belly heat only, but you would have a hard time keeping up ambient air temps with a screen lid. I use heat lamps the same as you, but I'm researching on building myself a lucylid. I will include links to the pages where it's shown. It's "almost" a completely sealed glass box that holds heat and humidity well. Also you can use bigger UTHs because the side of the tank is a bigger surface area than the bottom, and the heat has less room to travel up away from your snake. Do some more homework and reduce your temperature, but stick with your lamps for now.

http://ball-pythons.net/gallery/show...mageuser=15408

http://ball-pythons.net/forums/showt...arium-Solution