Would stainless bolts for the rudder assembly be an issue as far as corrosion? I'm thinking more specifically the 4" bolt that lets the rudder pivot...A good suggestion I saw somewhere on this forum is to place a piece of sandpaper on the mast with the abrasive facing out. Carefully rub the cleat base against the sandpaper to make it more perfectly mate with the radius of the mast.
There was also some discussion about fasteners. Apparently the stainless steel screws will galvanically corrode with the aluminum and seize in place. I'm not sure this is a problem, and I think I'm going that route. Never been a big fan of pop rivets and would expect them to work loose.