The advice given is probably your best bet,my gruman canoe took a hit from a tree and I bought this aluminum compound I'll call it,can't remember the name,but rolled in your hand ,almost a putty, stuffed it into the cracks and leaking areas,not one leak.
That was three years ago and you can sand it down. It was a tube and bought it at a local hardware Robinsons,and they swear by it.
Never leaked a drop.Great stuff.If your interested pm me and I'll drop by tomorrow and give you the name.Great stuff,easy to apply.