Fender rust help

I figured there's got to be some autobody guys or at least some guys with some experience with something like this.

I bought my 01 F250 because it was totally rust free, and it was until I drove it in the winter. Both of the rear fenders had small paint chips that when exposed to salt started to rust. What's the best way to deal with something like this? I've watched a few youtube videos on it but don't feel like I learned much more than I already know.

That's rotted right through the metal, so the only proper fix will involve cutting out the bad sections and replacing with new metal.  

cut out.. install fender flares.

done.