Will both wings fit into your painting space at the same time? If so, you don't need a jig at all. Simply pin them together using the spar pins and set the wings up on saw horses underneath the spars. You can rotate the assembly from top to bottom without too much effort and you can stand them up on edge too. That way, you can paint them both at the same time.
That's the way my wings were painted. It worked well. Just a suggestion.