Sometime back the center section was modified to include a handle cut from 1/4" 6061-T6 using water jet.
I decided to replace the original sheet metal tank cover with a new one which would extend back and tie into the handle.
Wood filler blocks were fitted and attached to the root ribs and blended to the contour of the center section around the leading edge and extending under the bottom of the wing. This will leave a very small gap at the nose of the root rib which can be covered with color matched tape. The GlaStar wing root is done this way as well as many gliders.
Here's the cut out for the grab handle in the center section.