Water proof caulk. West Marine sells a really good one called White Life Seal that sets up in about 24 hrs. If the holes are bigger, you'll need a thicker epoxy, but they'll be able to recommend something at West Marine. Won't last forever, but should get you thru a 5 hr tow. Would also be sure I had some inflatables to go under it if the worst happens and the pumps can't keep up.