I use heat cable on one of my melamine racks. I just taped over it with foil tape. The tubs still slide over quite easy and there isn't a huge gap between the roof and the top of the tub rim. Drill little holes on one side of the rack that are just above the surface where you are running the heat cable so you can go out one level of holes into the next. You will be able to use those same holes when you wire the heat tape. Possibly put a towel on the covering the back side of the rack where your cable is run to help with holding heat.