18" was the front to back measurement for that tank, and 12" was the height, which was why I was curious whether the height was anything to factor. The more I'm thinking about this I guess that would make the "30-gallon breeder" actually a 33-gallon, but given the focus on the length and depth of a tank over its height I'm guessing that the height is not as much of a factor.
Well, I'll just have to see what I have to work with space-wise (and possibly landlord-wise) and everything when I decide to get some BGs. I may have to wait a bit longer on these, but I will definitely keep what I learned here in mind when I do set to work on this tank. Perhaps in the meantime I can use it with customers at work.
Once again, thanks for the responses, Byron.