I've done something similar in the past and put a half rib near the end of the wing tube. I just cut into the sheeted wing after drilling the wing tube, slipped the wing tube through the half rib. After the glue dried, i sanded the half rib smooth to the wing surface and put 1/2" wide fiber glass over the seam to tie the rib to the sheeting. On the other subject of turning a one piece into a three piece. I'm considering the same thing on my Jupiter. I haven't quite figured things out, as there is no other way into the fuse on this plane.