I've had fittings pull out of the cabin top and repaired in the same manner you described with both fiberglass and West Epoxy. It worked fine with some big washers. For the Jib Tracks, you may want tape the holes in the deck and repair from inside the cabin. That way you won't have to sand the area where there may be non-skid. You'll need to add quite a bit of filler to the epoxy to thicken it to apply to the cabin top from inside. Or the new West 610 Epoxy is supposed to be pre-mixed and thickened. One word of caution, the epoxy sets up fast, so mix small batches.
KT