Man, that can open a can of works there. lol
All depends on how much time and effort, and what you want the finished product to look like.
The best way would be to treat it as a hull repair and glass it with smc compatible resin, then prime and paint.
The quickest way would be to find some rubber plugs and silicone them them in to water proof it.
Something like this.
Rubber Butt Plug | mudhole.com
If your not worried about ever taking it out, you could get a small tube of 5200 to seal it in. I think walmart carries a off brand, but I know Academy sports carries the 5200.