Im considering getting a sterilte tub instead of using my 20g glass tank. But I dont know if I can get the right thermal gradient. Right now I have a peice of 12"x11" connected to a johnson thermastat on the warm end, then a same size peice of flexwatt connected to a dimmer on the cool end. I have to do this to get a correct thermal gradient. Would switching to a sterilite tub fix this. Could I just use the one peice of flexwatt.