I have not made them both ways, but we build the racks so that the tubs go in long ways. Our biggest reasoningfor this, is they take up less wall space. We have 10 CB-70 racks, and needed more wall space.

I can say that depending on how you hook up your heat tape, when building a rack width wise, you could have a small temperature gradient. That is if you ran the tape under the entire back side of the tub.

Hope some of that helps,