I had a gap at the bottom of bulkhead F9 & F10 that I didn't think I could "squeeze out" with rivets, so I created spacers to fill those gaps. Here are some photos of the spacers. Notice that I am holding them in place with hot glue until I can turn the fuselage over and install rivets in F9 and the tail spring bolt in F10.
I found trying to get the bottom skin to stay in place at the flange was a challenge. I could not install a cleco or a rivet near the flange because I want to place the side skin on top of the bottom skin and attach the rivet through both pieces. The natural "memory" of the aluminum would flex the skin outward. You can not hold it in place with straps when you have to attach the side skins. I finally decided to attach an aluminum angle to the flange that spans the width of the fuselage at each bulkhead in addition to the angle in between the bulkheads (as called out in the manual) to keep it in place until I can attach the side skins. These angles will remain and don't add very much weight.
I will be cutting and trimming the sides skins in the near future. Progress is being made even if at a slow pace.