Okay, I got my tubs. I found some good sterilite ones at Wal-Mart with locking lids and a lot of floor space. Tomorrow I play to drill the holes into the sides, and set them up internally. I just need it answered as to, can I use heat tape on that shelving unit for my tubs, or if I need to stick with mats.
The ambient temp in my room stays 77 or higher

Yes earlier I meant thermostat. I don't know why I always type thermometer; I know the difference. If using heat tape and that shelving unit, I'd need it on two shelves with tape- one for my adult girl's tub, and one for the two smaller tubs for my young ones. When you say each string of tape, do you mean I have to use the same amount of tape on both shelves, or just that each strip I use to create a panel of heat on the bottom of the tubs have to be equal length? I was assuming the latter but I want to triple check.