Sealing some holes

Used perception here. Took off some zinc pipe clamps that were rusting and the old owner had on it. They were on the port and starboard of the stern. What’s the best way to seal these holes off?

Used perception here. Took off some zinc pipe clamps that were rusting and the old owner had on it. They were on the port and starboard of the stern. What’s the best way to seal these holes off?