I know of one -9A that had its wings built on sawhorses with no ill effects.
When I built mine in my basement, the floor joists above were exposed so I secured the tops to the joists and made some simple "feet" to keep the bottoms from moving.
Also, I did not use 4x4's but rather screwed 2x4's back-to-back to help prevent warping.
There is more detail
here.
I found that the pre-punched kits are so well engineered it would be very difficult to rivet a twist into the wing. Still, when it came to match drilling and riveting, I started in the middle of each panel and worked outward.
__________________
Bill R.
RV-9 (Yes, it's a dragon tail)
O-360 w/ dual P-mags
Build the plane you want, not the plane others want you to build!
SC86 - Easley, SC
www.repucci.com/bill/baf.html