The best way would proabably be to section that area out and butt weld in a filler piece flush with the panel's surface, which will be a lot of work. But in all reality I bet if you applied two good coats of epoxy over the bare steel then filled it with Everglass and finish with regular filler I bet it would hold up just fine. How sharp is the edge of this depression? It would be nice if you could make a cut through the center of it then hammer out the indentation, trim and weld your cut shut but I'm sure there is limited or no access in some areas. I think I'd probably just work the edges of the doors so it is eliminated in these areas then just epoxy and fill- I bet it'll hold up just fine. Maybe somebody will jump in with another plan

Bob