I have fastened heat cables under hardware cloth being careful that the cable does not touch or cross itself. I just tied the cable to the underside of the wire with string. It lasted for years. I would not recommend setting pots or anything else directly on the cable. I have tried burying the cable in wet sand with very poor results. The sand soon dries out and is a very poor heat conductor. Al

We use a sand bed with our heating cables, and depending on the wattage of the cable, you need to adjust the sand depth. For ex. our 25w hydrokable did not perform very well with sand that had a depth of 3/4" or more on top of the cable....at least for keeping our peppers toasty in a cool room. But, our 50w cable, easily chugs out enough heat to be buried a good inch under the sand and keep the pepper seeds at a toasty 80 degrees. We also do not keep our sand moist, in our experience the wet sand only made a difference (keeping things cooler) if the wattage of the cables were too low.
Also, I see no reason you couldn't use the cables on the wire shelves (at least the ones I use)...although I am thinking they will be a lot more inefficient due to heating the surrounding air as well as the wire shelves.

m