Jen,
My tubs fit snugly, but not so tight that I can't pull them in and out easily. The heat is a very important piece of the rack. You need to make sure that your tub slides on it's rails very close to the top, but at the same time, be very close to the heat tape. It is not hard to do, but takes patience. Measuements are important. Don't get in a hurry, and I'm sure it will come out great. By the way, I think that once you tackle that rack, it will be hard not to like it. Every time I look at any of my racks, even if I see something that is a little off, I feel a huge sense of pride and accomplishment in the fact that I built that thing with my own hands. If you need any help with your design or have any other questions, feel free to ask.
Sincerey,