It depends on how warm you keep the room. I do prefer the 11" for 41 qt. tubs, but it isn't going to do anything to heat the air so you may still have the same issue as you're having with the 4" tape. If the rack has solid sides and holds the heat well you may be okay, but there's no way to tell for sure until you try it. If the cool side still ends up being too cold, you'll have to look into some options to heat the room. I use a little DeLonghi heater and I've never had any problems.