You might want to go to Clay Davenports website and look at his page on "Wiring Flexwatt Heat Tape" and maybe "Cages Etc." When in doubt go to Mr. Davenports website it is an excellent source of reptile related information.
http://www.arbreptiles.com/
This is one way to accomplish the task. The way I do it, may not be the best, may not be the only way, just the way I do it. Enough said.
Your most basic thermostat has a temperature probe, electric receptacle, a controller and an electric plug for the wall. Your basic rack has plastic boxes in drawers with flexwatt heat tape someplace inside near the plastic boxes.
Tape the temperature probe to the flexwatt heat tape; a) somewhere so a drawer won't hit it b) not on the top or botton shelf c) using a good quality metal foil tape. I think this is metal high temperature duct tape, the glue side is backed with paper and when you tape something it doesn't come untaped on it's own.
Plug the flexwatt into the thermostats receptacle and plug the thermostat into the wall. Since this in in the BP forum I'd adjust the temperature to around 92F, now put whatever substrate your going to use in your drawers, add a few thermometers resting on the floor, front to back, top to bottom. Adjust the flexwatt temperature until your drawer temperature is what your want.