Here are a couple of pics of how I repaired this area. Since it is not visible, I did not attempt to recreate the original contours of this piece, I only wanted to restore the structure. I did attempt to make the repair in one piece, but found I was wasting a lot of time and sheet metal. Finally I made it in 3 pieces; a flat outer panel and two triangular fillers front and rear, and welded them together. Near the bottom of the repair where the pieces are joined, you can see a small gap which I left there for drainage. Hope this helps - Rodney.