Body Filler

I would not use regular type plastic filler over an area that has been patched from rust or on seams.
Body people don't like using All Metal or Fiberglass because it is much harder to work. Do the job as Dicer recommends and it will likely hold up well. I cant count
the number of slick pro jobs that look great for a few years only to crack and bubble
because all they use is plastic over everything.