I will give you a close up shot of how i recently did it for a rack that i build for fellow member Tony Lamanna. In the bottom of each rack shelf i routed a piece out exactly 3" from the back of the rack, 3-1/4" wide...to fit 3" heat tape, and exactly 1/4 deep. The tape enters from the side of the rack through holes that match up with the pieces that have been routed...from there it simply slides under the dividers..out one side and to the next shelving row. I was told that placing the tape at the back gave the animal a choice...basically hot...or hotter
Hope this helps