Not all stainless is, or will hold up the same, especially depending on what chemicals it's exposed to. (But it will be more durable than galvanized.) Try to get stainless that is not magnetically attractive.

well all i have found is 304 stainless 2 inch..and I'm starting to like it but not sure.

I would talk to folks in your area with similar projects. All I know is that salt air is brutal, even on stainless steel. We're a dealer for stainless steel outdoor cabinets and we won't sell them to anyone coastal unless they opt for a protective clearcoat. I have no idea if a layer of concrete board and stucco or tile is enough to preserve the framing in your climate, but if it were my house I'd do masonry unless there was a reason I couldn't (deck, rooftop, etc)

I think he is saying he doesn't have salt air. Maybe not.

John Doe, ask a metal expert about the durability of 304.