I would make a simple box structure between the spars that runs to the 3rd rib in each panel and make a ply dihedral brace that will fill the box and that will slide into each panel. You can make one for the front and rear spars, once you slide the wing panels together and attach them to the plane the rubber bands will hold the wing halves firmly together. I assembled a Senior Telemaster ARF for a guy about 10 years ago that had this setup and it worked great.
I wish I knew how to draw diagrams on the PC and I would show you.
Anthony