I just finish building my new rack system im using 12 6.5qt tubs on 4 shelves and instead of using heat tape or heat mats i used 1/4 copper pipe i cut groves on the ply-wood and ran 2 pipes about an inch apart and have them all running down to a 5 1/2 with a submersible heater keeping the temp. around 90 degrees in the fish tank. I used foil tape under the tubs so that i can dispense the heat and i have a good heat of 85 degrees to the tub. will post pictures in a few.....