I have a suggestion, you could clean out the pits completely and cut a thin piece of sheet metal to cover the area (like 24 ga) then bond it on with 3M 08115 Autobond adhesive. Make certain that you cover the whole piece and get some into the holes. Then skim it with filler. If you do it on clean metal it could last the life of the car.
I've used this stuff quite a bit. (steel to steel; fiberglass to steel) I bonded two pieces of 24 ga together and tried to tear them apart and the metal tore around the bonded area without breaking the bond.
I use this to repair rusted 1/4 pnl edges and door skin edges.