In actually seeing the rusted area, it is significantly worse than you were initially describing or at least what I was interpreting. That area needs to be cut out and replaced if you hope for it to last a long time. I envisioned something more local from your initial description/photos. In other words, you will not likely ever be able to get to solid clean metal over the whole area since it isn't localized much at all.
I have had a couple cars that had localized rust just around the trim clip threaded studs and not anything pervasive like this. With the localized rust my suggestion was doable but not with this IMO. Its at a metal seam so this requires a different approach.
I have had a couple cars that had localized rust just around the trim clip threaded studs and not anything pervasive like this. With the localized rust my suggestion was doable but not with this IMO. Its at a metal seam so this requires a different approach.