Shaped Hatch flange foam, sanded to thickness and applied 2 x UNI @ 90 degrees.
Cut flox corners inside NG-31 cutouts, and at the outside edge of the doublers. Tool of choice is dremel, with 3 exploding grinding discs on the arbor.
Floxed 'em up, then hot glued NG-31 to F-0 (taped), supported on a workbench, with packing. Layed up 2 x BID over all