Stainless bolt/nuts are just fine. I've used them on all kinds of boat problems since the 60's.
Stainless above the Water line, Bronze below!
I riveted wings at Boeing.
We used 'soft aluminum' solid rivets for most of the long runs along the stringers. Certain places had Titanium's that were swedged. You do need a special gun for those rivets.
The Soft rivets took two of us, one driving and one bucking. The Bucking bar was especially designed to mushroom the rivets without destroying the Wing. (Boat in this case)!
That would be the best of all worlds if you could get the stuff to make it work.
Now days you can get "Pull Rivets" and "Drive Rivets" in all sizes and hardness'. Go to the OTR Trailer re builders and they'll fill you in on the good rivets.
You don't need an air gun. Although it would sure make it easier.
My 12 yr old son was my Bucker on this old Star-craft boat.
I made him a Concave bar. I Batted the rivet from the inside, and he held it tight from the outside. It worked pretty well.
He hated me and wouldn't come home for a week after we got part of the boat done. :lol: A kid can only stand so much of that, so we did the boat in sections. It took four 'efforts' to get it all done.
If I can help more, send me some photos.
Dick