Riveted on the upper side skins via back riveting. The first side you can reach across and set the rivets without much trouble. The second skin requires someone to get inside with the back rivet set while your helper holds the back rivet bar on the outside. I took a bunch of folded up moving pads to fill the bottom space and prevent any bending of the formers while I was in there. We managed to finish both sides and get the top center clecoed in place to back rivet on tomorrow.