For the 1" holes I would use a wood dowel slightly larger than the hole, cut a piece so you can tap it in the in the hole and leave about 1/4 " below the top cap to put gelcoat in.
Cut it so the bottom of the plug is about even with the bottom of the cap. Coat the plug with resin or gelcoat and tap it in . Fill with gel to slightly over the top to allow for shrinkage.