Recleaned all surfaces associated with the inner & outer ribs. Working on one tank at a time: (1) Applied sealant to ribs and clecoed in place. (2) Penny inserted rivets and I squeezed them w/ the pneumatic squeezer. Had to replace one w/ a 4-4 Oops rivet. (3) Installed stiffener plates on inner rib and riveted into place while Penny bucked. (4) Installed fittings for fuel tank vent, flop tube, and BNC connector, secured nuts, and sealed into place. During clean-up, connected fuel vent lines and flop tubes to tank fittings. Cleaned up everything which took 1.5 hrs alone.