Actually, Optimas are not gel batteries. They use conventional liquid, but there are absorbent fiberglass mats between the plates, and the acid is contained in this matting. Thus there is no "loose" electrolyte to leak out. Batteries like this are called AGM (for absorbent glass mat) or starved electrolyte batteries, and they are classified as "leakproof" and are shippable by normal methods. I actually recently bought one mailorder for my Miata (I know, I'm a pussy!) from these guys:
http://www.1st-optima-batteries.com/ and was very happy with their service.