I searched this forum and didn't find anything on this. Hope I'm not stating the obvious.

Had some not so great cutting from a kit cutter and after adjusting wing incidence had some gaps that were pretty big in the saddle. Here's what I did. Worked great and a perfect match.

Rough up the edge of the saddle with 60X. Denatured alcohol to clean and prep. Spray a light coat of 77 adhesive on wax paper and attach wax paper to outside and inside of fuse at the saddle cut. . Trim wax paper flush following the irregularities with a sharp blade. Just want the saddle edge exposed here. Attach 2 layers of wax paper to the wing.
Apply generous amount of Bondo to the saddle edge. Nothing fancy, but squeese a skim coat first to help hold the Bondo on the edge. No big deal if some goes under the wax paper. Put wing on and bolt down. Push the Bondo into any voids . Scrape off some of the excess if you want but don't cut the wax paper. I scrape off with a balsa stick.
Let dry and after removing the wing pull off the wax paper and cut, file and sand flush to fuse sides.

Even easier: tape a piece of garbage bag plastic, about 2" wide, over each side of the wing where the saddle touches the wing. Then mix up epoxy and micro-balloons (or your Bondo should be fine) and put a heavy layer on the wing saddle. Bolt the wing in place and use a balsa "paddle" to wipe off any excess that squeezes out past the fuselage side, so that the mix is flush with the fuselage side. Let it all dry. Take it apart, and use a sanding block to sand any remaining protrusions flush with the fuselage side. Use a sharp knife and remove any excess flashing on the inside of the saddle. (With enough micro-balloons, you can carve the stuff pretty easily).

Clair