The instructions state that you should use a "large weight" to hold the skin flat on the second side when drilling and clecoing. The picutre looks like a wooden door. I used a nylon strap instead with a wooden block in the rear spar channel to keep it from bending. It worked well.
Leaving the trailing edge and tips un-riveted to allow fitting of the elevator hinges and the fiberglass tips.
Going to need more clecos when we get to the wings.
The best part of assembly; riveting. It goes quick with the pneumatic riveter.