One easy way to repair both the leaks
and the sag is to remove the top and take the shell to a fiberglass shop that has a "Chopper Gun". They can shoot a whole new inside liner, up to about 1/2" thick, and also put some bow back into the roof. I have had cracked holding tanks encased in this manner. You might start with a local boat repair shop.
Short of that, you can remove the top and recoat the entire inside with resin, that will at least stop the leaks
. You can buy Bondo brand resin at most auto supply stores.