Thanks for the help, everyone!
Sooo, it turns out the same guy who had the 55 gallon tank happens to have several more unused tanks in his basement, including a 10-gallon and a 20-gallon. I guess for now I'll go with one of those! I was just hoping to go with one big enough that I wouldn't have to "upgrade" as the snake got larger, but it looks like that's not the best way to do things right now. Guess I'll be returning that 40-60 gallon under-tank heater after all! :oops:
Well...all right, secondary question, then:
Argentra sent me a pretty excellent thing all about setting up a good habitat. Sez "A baby should be in a 10gal, a juvenile in a 20gal long, and an adult in a 30 gallon or nice display cage."
Is 20 gallons still stressfully big for a baby? How quickly will a baby become a "juvenile"? That is, how quickly will I have to replace the tank?