Match drilled the cover to the control mount with a #19 bit. Also match drilled the holes at the aft end of the cover thru the floor and longeron to #19. Used a nut plate jig to drill for the rivets. C/S the control mount and the longerons. Squeezed in some 3-5’s to secure the nut plates to the control mount. For the longeron nut plates, I used some small cherry rivets (CCR-264SS-3-2’s). I plan to cut off the flange where the vent would have been attached. Won't need it as I'm using one of Steins vents thart screw together thru a hole in the cover.