I was taking out my driver side headlight to fix it, and was allowed a rare glimpse of the inside of the fender down there. (See attached pic). What is that white powdery substance on the fender? It feels like dust, and it could be road salt, I guess, left over. But I had that fender reconstructed by a body shop a few years ago, Could the white stuff be something left over from the body work?

Also notice the rust in a few spots, particularly around the nut that connects the thin support bar to the fender. Would treating this rust with POR or some other rust inhibitor slow it down or stop it?

Thanks

 

I would wire brush, clean w/acetone and por it. Por is perfect for areas that dont see uv.
Just remembet por needs rust to stick.