That would be much thicker than store-bought tanks, and I would even be able to treat the inside with rust-prevention compound -- like the rust-proofing they use on cars.
I think to bend the steel into a cylinder would be very difficult, so the best way to do it would be a 16 X 16 X 48" box, which would be about 53 gallons.
I know that a square box isn't as strong as a cylinder, but with 1/8" steel, it should be overkill, right?
What do you think? Criticism and suggestions are welcome!