I'm a bit confused as to the instructions for mounting the Gretz mast. The confusion involves the holes common to the backing plate and the supporting angle. The instructions seem to state to drill these holes to the skin as well but then state to use flush rivets to rivet the backing plate to the angle without mention of the skin. This would leave open holes in the skin along that rivet line. If the skin does need to be riveted to both the backing plate and angle along that rivet line would one dimple the skin and countersink the backing plate to accept the dimple or countersink the skin?