The cabin top construction: a layer of fiberglass, plywood or balsa, and another layer of fiberglass is all part of the structure that keeps the cabin top stiff and strong. I wouldn't (didn't) skip the interior layer of fiberglass.
I'm sure my problems started wit too many holes drilled into the cabin top. The correct way is to drill a bigger hole, fill it with epoxy, and then screw into the epoxy. A little more work up front but saves $$$$ and times later.