Tonight I trimmed, smoothed, Alumiprep'd and Alodined the fourth tank inspection plate, then riveted more nutplates. Just two more large plates left to make, then six doublers for the outer edge. I'll install both sides with ProSeal, holding the inner plate (with nutplates) in position with a valve-grinding dopstick while the screws are inserted. Beforehand (obviously), I'll be able to reach inside each tip tank compartment to reinforce the wall seams and apply ProSeal for extra confidence in the edge seal.