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