Riveted the left HS skin in place. Had to ream out a few holes along bottom trailing edge. Took extra time to ensure rivets grabbed correctly for the two smaller leading edge ribs as these were more difficult to get the holes aligned correctly when installing clecos. Also check that front spar channel center angle (third layer) was seated properly when rivet installed vs being pushed down. The inexpensive borescope was very helpful to look inside the structure once the skins were already cleco'd (https://www.amazon.com/gp/product/B07ZVF6HX5/ref=ppx_yo_dt_b_asin_title_o07_s00?ie=UTF8&psc=1).