Removed bottom skin again, and installed rivet in the lower longeron to connect the 902 bulkhead in each side. That would have been very tough with the bottom skin in place. Replaced bottom skin, and riveted some rivets in the longeron to side skins that I could squeeze. Most of the rivets for the longeron get riveted later, when the top skins go on. Riveted a few other rivets around that I could do by myself. I need to find some riveting help soon.
