I just realized I can't get the 6" heat tape in Canada. Only 4" or 11-12". I have some more planning to do.

I don't know that 4" is going to be enough for the 41qt tubs. I will be keeping this in a living room that is 68-70f. That is why it will be a closed rack with doors. I will have some ventilation of course.

It has been suggested by some on a similar position that I need 11".