Drilled upper, inner and outer skins with wing walk doubler to final size. I used clecoes every 3rd hole on the entire skins and spars to make sure I had no movement. I also dropped my plumb-bobs at the inner and outer most ribs and took measurements to the rear spar. It measured exactly 2 5/8 inches on both. I was pleased with that, knowing its perfectly straight before I drilled holes to final size. I used boelube when drilling.