On my current Scamp
project I replaced the larger rivets with 10-24 pan head stainless screws. I used a cap and sealer on the outside and a flat washer and nylock nut on the inside. I have an ensolite liner and if course 1/2" screws were a little short and 3/4" screws were a little too long so I have ordered some 5/8" screws.
I found acorn nuts to be very expensive relitive to other options especially the stainless ones. Also with nylock nuts you can better control pressure on the fiberglass
verses using lock washers with acorn nuts. Also if you your screw threads extend to far you can dab just a small amount of clear silicone to cover any exposed threads.