So, there are many rack systems but these are the ones that I use: http://www.reptilebasics.com/Reptile...p-1-c-251.html
I use these because they are already built (I am not a carpenter) and they are enclosed. Some rack systems are open on the sides, but I don't have a temp controlled snake room, and so I appreciate the top and sides helping to hold in the heat!
The heat in the racks is provided by flexwatt and is run at the very back of each tub and zig zagged up the side and into the level. The tubs sit over the flex watt.
I use 2 brands of thermostats and both are very good: Helix and Herpstat. I just hook a Helix up to the flex watt at the back of one of my racks (one Helix or Herpstat controls up to 6 of the racks that I have [the 4-drawer sweater box]). I set the thermostat to 93F and the thermostat then keeps each tub at 93F +/- 3 degrees, depending on the location of the tub (the bottom tub is about 90, the top tub is 93).
I have an Acurite thermometer/hygrometer in each tub to measure humidity for me and give me an overall ambient temp inside each tub. I use an infrared temp gun to spot measure gradient temps within each tub.
Does this help you, or have I done such an abysmal job of explaining that I have accomplished nothing more than to further confuse you??? Let me know! Take care.