I left the loose rivets in used wire brush on my drill to clean and scuff around them then JB weld been 5 years no leaks cleaning the area good is the key no matter what you use
Same here on last jon boat I owned. You can smooth the jb weld marine sealant out by getting your fingers wet with water and smoothing it out over the rivet as soon as you put it on with flat tool of sorts after mixing it.
PROUD MEMBER OF TEAM GEEZERauthorized by: Billbob and "G"