I've had paint pitting from using JB Weld on body work. It was a plastic fairing. So no fillers with metal in them. If the rust pitting is bad just use a body filler, they have body filler with fiberglass as well for extra strength.
I would never use actual fiberglass over steel, to patch anything.

Kicking self for selling off my Taskforce trucks.
Still looking for an LCF or conventional big bolt in decent shape.


As of 10-26-2022, A 55.2 Taskforce long bed now the work begins