I have a 5 tub rack, using a herpstat with flexwatt belly heat. I had a thermometer in each tank until the snakes started knocking them down all the time. Now i only have 1 tub with a thermometer and never have any problems. As long as all the tubs are set up the same, i dont think u have to worry. I like belly heat the best, then they have something to lay on that is direct heat, but back heat works.