How big is your heat source under the tubs? I built my rack with 41 qt tubs, fully enclosed walls, and designed to go in a bedroom at normal room temperature. I used THG heat tape cut into 12"X15" pieces to ensure a LARGE surface area where the heat emits from to make sure ambient temps stay up. And it does so very well. You really wont know how your rack will do until you get that thermostat in. If after that you are still low on the ambient/cool side of the tubs you can try adding a curtain of thick cloth or a door of some kind on the front of the rack to hold in ambient heat. I planned for a such a modification, but luckily I didn't need it.