RE: common mistakes ??
Do not try to catch a dropping xacto
Do not try to catch a dropping xacto with your leg either.
Making 2 left wings causes you to make 2 right wings.
For the weight to hold everything in place, I make up several zip lock bags with 4, 6, or 9 scoops of sand in them. Fold the ziplock side down and I use rtv to keep them shut.