I put my probe directly on the heat tape because the temps are less apt to changing. For the aluminum I use metal tape for under the flexwatt and then cover the edges of the flexwatt with the tape as well sticking it down onto the other metal tape thats on the bottom. Did you soder your heat tape or do you have clips? Also make sure to fully cover where your connection to the wires is with metal tape as well. If you type in flexwatt on youtube theres a bunch of good videos, everyone does it a little different. If you have any questions let me know.