i found this info on this site, and that's how i set up my tank. seems to be working really well.
"What I used for my old 20L tank, since I had to use two UTHs was:
I got a Repti temp 500r and two Lutron 300W dimmers. Plug UTHs into dimmers, set temps to 95 and 85 for warm and cool side, respectively. Plug dimmers into thermostat and set dial to appropriate level. This way, both a warm temp of 93ish and cool of 83ish are maintained."
the cheapest place i found for the thermostat and UTHs was, oddly enough, better homes and gardens' store
http://shop.bhg.com/category/1131/1/reptile.html
the rheostats (dimmers) are $11 or 12 each at lowes.
i insulated the sides and back with black foamcore and covered a little over 3/4 of the screen with plexiglass from a picture frame. i cut 2 pieces about half the size of the screen section. so half stays covered and the other one can slide open or closed more depending on what the humidity is at.