What is behind the screws for the rear loops?

I decided to mess with these eyelets that are on the back of the sunfish. The one screw head broke off.
I got two others out fine. These are not wood screws but some sort of self tapping machine screw. This is a 1998 era Person built hull.
I am making an assumption it is just going into thick fiberglass.
Does anyone have experience with this problem and which solution works?

thanks