Thanks for your inputs. I do need to remind you that I am not using Flexwatt but a heat cable. There is no room between the heat cable and the tub to place the probe. The rack I bought has six rows of maybe 6 inches of heat cable per shelf and the temperature in that area is so much different than the temperature of one row of heat cable (that is routed to the hot side of the tub).

I hope I'm clear?