#36 drill bit and 6-32 tap used to tap the 16 holes drilled through the skins and into the longerons.
Decided to use only one hole on the aft end of the covers and into the cover plate.
Countersunk the skins/longerons and dimpled the side covers. Right side completed, left next.
Dimpled the frontmost hole but realized afterwards it is covered by the fiberglass empennage fairing. Un-dimpled it.