Glassing the hull to deck
joint from the inside is probably the easiest if you can get to it. You will still have pull the toe rail and drill out the rivets as they will make it very hard to get the fiberglass to bond properly. Use epoxy
resin, Polyester resin just doesn't bond well to old laminates. Pearson
built my boat with the joint glassed on the inside. Unfortunately, they used sheet metal screws and Dolphinite to install the toe rail. The Dophinite has hardened over the years and lost
it's sealing ability, suspect the rail wasn't sealed all that carefully to begin with so had numerous leaks
from the fasteners.
Can you tell whether the leaks are coming from the rivets or is the hull to deck joint suspect?? If the bond between the hull and deck is compromized, you've got a major headache. You can pull all the fasteners, pry the hull and deck apart, clean out all the old caulk, and reseal with Butyl, 5200 or LifeCaulk. If the original sealant
was Dolphinite or some other oil
based material, you've got to get it all off and thoroughly clean with acetone or the new caulk won't bond. The other choice is glass from the outside but that requires the skills of a good glass person to get the new laminate to blend in. If you are good with glass or want to learn how to, it's not an overwhelming job on a boat that small.
Good luck with the projects. Hate leaks. Nothing makes life at sea more miserable than a soaked berth.