You attach the bottom skin next. You rivet it just like the top but this time you have to get your hand in-between the two skins.  It’s a little harder to do but not difficult.

With that done, you double flush rivet the trailing edge, squeeze the rivets on the outside ribs to the skin and then pop rivet the counterweight to the leading edge skins. Then you hang them up where the Sonex ailerons waited to be installed. They are a little bit longer!