Stainless rivets will work fine - you definitely need something stronger than aluminum for those jib lead cable padeyes. You can also use screws and nuts if you wish (glue the nut on the end of a stick to get it started). Stainless rivets do require a bit of hand strength to set, but you can look at it as a hand strength exercise. I set 48 stainless rivets on the Team Seacats N20 when I rebuilt it last year using a run-of-the mill hardware store rivet gun. In order to get it seated well it is important, when setting any rivet, that you keep good downward pressure on the rivet to hold it flat against the outer surface..stainless rivets are especially sensitive to this.

I always put something under the rivet (even aluminum rivets) to seal them up and provide some barrier. 3m 5200 will serve this purpose well and while I'm not sure about how much it prevents the two metals from electrically connecting, it does prevent water from getting in and sitting in the joint. Once you've set the rivet, you can clean up the 5200 with mineral spirits for a very nice clean smooth look. You can get 3M 5200 in most Wal-Marts in the boating section.