I wouldn't call the gulf coast rust a major problem. Mostly light surface stuff. If you want to see rust, look at the Jeeps from the North or anywhere else they put salt on roads. Sea air won't cause structural damage but road salt will in a relatively short time.
Always check for rust though... you just can't be sure where the jeep lived. Rust and modifications, especially the mods that are done cheaply or by some good ole boys at deer camp using pipe wrenches, create value loss. Rust free and unmodified YJ's are out there. You just have search for them.