What are your thoughts on rivets being used through the hull, as in the Clipper designs? How would a leak be repaired, with a bead of epoxy?
I’d be concerned about using rivets below the waterline. Impacts/scrapes from the outside might tend to loosen them and result in leaks. Above the waterline, I wouldn’t be too concerned. Any leaks that might occur would likely be minor and result in no more water entering the boat than that which might drip off the paddle, or result from a splash.
Depending on what you want to mount, you might be better off using stainless machine screws and nuts along with nylon washers. You can add a bit of silicone caulk/sealant to waterproof the holes. I wouldn’t be too worried about a lot of water leaking in. A huge number of whitewater kayaks have foot braces attached with stainless hardware that goes through the hull below the water line. Yes, a small amount of water might leak in over time, but not a lot.
If you don’t have inside the hull access, or access is difficult, well nuts work great. The rubber on them expands to seal up the hole & secure the screw.
go with well nuts easy cheap and work great.
Pop rivits leak. Properly “bucked” rivits like on those old Grumman canoes of the 60’s don’t leak…right away. Most people don’t have the tools to properly set rivits like an aircraft mechanic or the skills. Go with machine screw, flat head or pan head with nut and washer. You can seal the hole, head and nut with 5200 marine sealant. They won’t come off either.