Marking locations and using weights to laminate the 1/16th ply inner sides to the 1/8th fuselage sides is a typical procedure for many model aircraft. Being sure that one makes a right and a left side. I do this step together for both sides at the same time so I don't make the mistake of two Left or Right halves.
The next image is adding the 1/8th x 1/4 edging longerons in place after the fuselage sides have been completed. Lots of test pinning, weights and test fitting along the way. These steps came out reasonably well.