I used a flap sanding wheel in my electric drill to thin the outboard forward corner of the inboard skin. This is where the top main skins overlap and this should make for a smoother transition between the skins and the tank. Once this was done, I deburred the edges of the inboard skin, sanded them with emery cloth, and then polished them with a red scotchbrite pad. Then I broke out the C-frame dimpling tool and the foam and dimpled the inboard top skin.. Once this was done, I primed the inside of the skin where the wing walk doubler will be on the inboard edge, and where the main skins overlap on outboard edge.
Sanded joint where top main skins overlap - inboard skin
Inboard top skin dimpled
Prime inboard top skin for wing walk doubler plate
