[njsteve]

Grind all the paint off with 80 grit. I would then cut a flap that fully exposes the rusted area. Grind the rust away and prep it properly and then use the 2-part urethane rubber bumper repair stuff as a glue to hold the flap back down and clamp it in place.

I have done the same with Cuda rubber bumpers. They all had a habit of breaking off the sealed-in bumper bolts and you had to do similar surgery to replace the bolts.