Alot of people build their own racks, which I did and I love it. A majority of racks use heat tape, which you MUST have a thermostat for. When a thermostat only has one probe it can only control one type of heating element of that wattage. So for example I can't hook up 6'' heat tape and 12" heat tape into the same thermostat cause they use different wattages, get what I mean? lol Then if I have a thermostat with 2 probes I can control 6" and 12" heat tape just fine.

Heat tape is just best for racks cause it's easier and takes up less space. Racks though you have to keep the air warm around them cause you only have the heat tape on one side, so if you're room is cold you'd have to get a space heater.
BUT, you can have multiple strips of the same sized tape on one thermostat, you just have too plug it all into a surge protector, then the surge protector into the thermostat.

For example I have 4 strips of individual 12" heat tape for my rack, plugged into a surge protector, then that plugged into the herpstat 1 i have. Making sense? haha