I keep my aluminum boat in the salt year round, no problems other than bottom paint is kind of special. It's true that cosmetically the aluminum will eventually get a chalky look to it but so far after 3 years mine hasn't changed much and there are certain types of detergents that will re-brighten the surface if you're fussy about it. I've seen corrosion problems with boats that have strips of aluminum angle iron skip welded on the bottom to create lifting strakes (like on a Wooldridge) if left in all year.