Stainless isn't necessary in saltwater. When I had a marine canvas shop we used polished marine aluminum tubing and cast aluminum (not plated zinc) fittings in saltwater. 10 yrs later you won't see much difference on the tube (it still shines) and the fittings will have microscopic corrosion that only takes the original dull shine off. The fittings have SS lock screws that will freeze up in time if you don't use antiseize on them. Once a year cleaning and lubing will keep aluminum looking good for many years. The main reason I would use stainless is for strength and/or "yacht club" appeal. On small boats people grab the bimini frame as a support while stepping around in tedious conditions. Aluminum will flex more. Also...My M-10 dink survived hurricane Frances without a scratch. I stuffed it (upright to hold water) deep into dense woods and tied it to big trees. Hurricane Ivan is heading this direction so it's staying put. I'd hate to lose this dink after owning it almost 30 yrs. BP