Sig sends an aileron gage in the kit, die cut piece of ply. It works off the top of the wing.
BTW I use 2 rubber bands on mine, no problem. The hooks do have to come through far enough or it's a pain.
Tip: I cut a long dowel for the back holes and use it and the wing pipe with a rubber band to hold together for transporting on my rack.
This plane is a blast!!