just want to add that, my room temp is at about 77, and i have tried to put the probe directly on the heat tape, and i could not get the temps high enough.......once i moved the probe just an inch in front of the tape it worked out great!
i know a lot of people do it different, so i would suggest checking out what everybody else says, and making a choice (but this was the way i had to do it)
i hope this helps