I have human heating pads under my rubbermaids. I like them better than the reptile ones by Zoomed that I have...the zoomed ones I measured at 130 or above (painful to touch) without a thermostat. The Walgreens human heat pads I have get to the mid 80s (nice soothing warmth) on the medium setting (and they're cheaper). In a rack I would probably use flexwatt heat tape. A temp of 130 will not melt rubbermaids, just so you know. The inside of a car easily reaches that temperature on a warm day.