Disco 1 early front bumper rust repair?

Front bumper has got quite rusty towards the edges, outboard of the mountings. Not much chance of finding a decent s/h one (if ebay is anything to go by). Can probably repair as most of it is hidden behind the plastic corners, anyone done this? Plate behind then either chemical metal or plain old filler to finish?

Yes I had to repair mine as no suitable replacement was available, I brought new end caps as there was no way to salvage them,
Then quite a bit of 1/8 plate to repair finish with Matt black,