Then it seems unusual to me that people do this if that is the case. I have seen it recommended on here to cover the outer edges and I recommend it to for obvious reasons. Maybe you're right about covering all of the heat tape and I've personally never done that but I have put a strip just one tape roll width along the 2 ends (front to back) where the bottom lip of the tub rubs lines into the heat tape. In my opinion, this is much safer than wearing through the plastic covering the wires of the flexwatt, thus exposing them creating the possibility of shorts, fire, and who knows what.