If it were me I'd stuff the foam noodles in the gunnels before I added anything permanent. The foam around my original fuel tank was the reason for it rotting out.

Take out the rod boxes and stick your hand down below the floor level just under the forward rod holder. You should feel foam. Should be able to see it with a light. If your rod holders aren't plumbed to the bilge the foam is probably WET if it has sat out in the rain.