On the hull there are two layers of fiberglass/epoxy sandwiching some foam.

You have to repair the two layers and replace the foam. Start by sanding the outer layer, remove the broken foam and repair the inside layer. You will have to remove quite a bit of material to give you enough access. Once the inside skin is repaired replace the foam with a mix epoxy/light filler and then rebuild the outside layer.

Finish up by spraying gel coat. And sanding. And more sanding.

Don't ask me how I know

As for the inside of the daggerboard case I suspect it is a single layer of fiberglass. You problem there is access. I've heard some stories of fixing such a problem by creating a small vacuum in the hull and dripping epoxy so it is sucked into the crack, hopefully sealing it. Probably worth a shot.