Work on the elevator spar and ribs. One big mistake was that I riveted the top of the spar together in the center before installing the reinforcing plates on the top and bottom. So I had to drill out eight 4.8mm rivets. Fortunately, Sling is really good about sending you more rivets when you need them as long as it's just a few.
I also misinterpreted Evan's advice about not dimpling the outer row on the forward skins until you have fitted and match drilled the composite tips. I heard don't dimple anything out that way. After the outer rib is in place, it is very difficult to maneuver it into the drdt2 dimpler, so I just used my 3D printed dimple dies, initially with a normal vice grip. But...