Thanks Larry!
What will you be keeping in the tubs? I used to keep all of my adult medium sized New World colubrids in 20 gallon tanks, until I had too many tanks for my little snake room. So, I reluctantly started keeping some snakes in tubs, and eventually started keeping almost all of them in tubs.
The area of a 20 gallon tank is 360 sq inches, which I think is a decent amount of space for the avg adult corn, Emory's, king, etc. The avg 28 - 32 qt tub (which some companies call a "boot box" ) is somewhere around 23" x 15" = 345 sq inches, which is still a decent size for corns and smaller kings, I think.
For colubrids up to five ft long (Baird's rats, etc.), I use the Sterilite 41 qt tubs, which are somewhere in the neighborhood of 33" x 15" = 495 sq inches. Iris makes a tub with similar dimensions as well.
I will keep baby corns and some species of rat snakes in shoeboxes until they are about a year old, and 12 - 15 qt tubs from one to two years old.
I throw these loose guidelines out the window when it comes to certain species and types of snakes - like Beauty Snakes. The largest cages which I can fit in my snake room are 24" x 36", which is what I keep my adult Chinese Beauties in. They are a smaller subspecies of the beauty snake group, and only around 5-1/2 ft long, but are quite a bit more active and racer-like than the avg NA rat snake. This is the same size approximate floor area of tubs that I would like to use for a rack for these. As Chris mentioned, Iris makes a tub with this floor area, but it is only about 6 inches high. I prefer to keep these snakes in cages with at least 12" vertical space, with some objects for climbing on.
Snake keeping and husbandry is a really personal thing, for lots of people, and there are some who would say that the tubs and cages I keep my snakes in are too small. There are also people who keep all of the snakes, I have mentioned, in smaller accomodations, and they still seem to thrive. I know an old school herper who keeps most of his adult colubrids in 10 gallon tanks. The thinking here is that a well adjusted captive snake really does not move around the cage much - which I happen to (mostly) agree with.
I don't think I have anything useful to say about heating, as I live in subtropical south Texas, and I use very little supplemental heat. I have back heat for most of my racks, in the form of 3" Flexwatt down the pegboard backing. I used it for the first time since early spring, last night, on one of my shoebox racks, after feeding some baby corns. Early spring is the time I use the heat tape the most, when warming animals up from brumation. I also keep a few species of Eurasian rat snakes, which I hardly ever use heat for. My problem with these is the opposite - keeping them cold enough during the winter!
Hope this helps a little - I get long-winded sometimes (too much coffee 
)...
-Toby
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Southwestern Center for Herpetological Research
to get a rack into my snake room (and expensive too). If only someone made a tub that was ~ 20"-24"W x 36"D x 10"-12"H...
