Heat tape won't do much for the ambient temp of the rack - maybe a degree or two, but that's about it. When there's a big as of a difference between the room temp and your goal ambient temp (which should be around 80), what you really need is an alternative way to raise ambient temps when using a rack system. Personally, I have a oil filled heater hooked up to a thermostat to keep the snake room's ambient temp from falling below 78.