The easy way would be to use a little clear silicon. Put clear tape on the bottom and apply the silicon to the top. If you want to repaint the top, then I would use fiberglass.
I have similar top on my pontoon...it had 4 or 5 similar holes...used alum tape on underside and found a gray colored caulk and applied from topside and smoothed it over with my finger...it worked very well and from a distance almost impossible to see...hope this helps
Thanks for all your replies.
I remembered that I had a tube of "Marine Goop Adhesive/Sealant" that I had got from West Marine. I put some tape behind the holes/cracks and filled the top with the goop. I used it before on other things and it worked great.
