looking good there well done! I would suggest making a straight strip with the angle folded and longer than req, For the bends by snipping Vees out of the base part it should pull round the corners, Whilst carefully brazing, as nec, any of these these V cuts that show( after finishing would be covered by the rubber) Also may be poss to find something in the scrap yard to match the strip profile I seem to remember a common car with similar , If I were doing it I would cut the showing rust holes a bit bigger and braze ( less heat and does not rust again for a while) small overlapping plates fitted behind, This should eliminate any thin area round hole, Keep us up to date.,