Tape the probe directly to the heat tape in the very corner of one of the shelves. The tubs i use are slightly tapered (sp?) so there is a 1/2 inch gap between the base of the tub and the side of the shelf where the probe won't effect the tub sliding in and out.
yeah the tubs Im using are 41 qt sterilite sweater boxes and they are tapered, so I should tape the probe on the corner of the flex watt?