Ok so lets say i have a rack with 9 tubs, 3 per level. I would start the flexwatt at the top and make it go back and forth till it ends at the bottom.

Do I only need one thermometer, placed in the center cage? If one cage is below temp, then the rest must be as well?

If the temp reads a few degrees below normal, and the thermostat makes the heat kick on, it's going to heat every single cage...is this what I want to happen?