By the way, what if I were to put two strips of electrical tape (those used to seal off the end of the flexwatt where cut), OVER the two strips of metal along either side of the flexwatt? (i.e. I lay the flexwatt down, I over the two strips with some electrical tape, as "extra" insulation in addition to the thin plastic laminate, then affix that on to the shelf with foil tape.) It is largely those two strips which concern me as they are slightly raised and thus can rub more, and also they conduct the electricity so I don't want them to connect with the foil tape in case there is a scratch on the plastic.

Would those two strips over the metal parts cause problems?

I just want to find an alternative to protect the tape instead of covering the whole thing with foil tape because I have been told here that it will cause the mat to heat up too much and not much heat get to the tubs. I am also just paranoid that there are small scratches on the plastic exposing the electrical components which I can not see.