Outside above the fender, I hear it's common. Are there patch panels, whole panels, what's available? Just bubbles right now so I don't know what's going to show up once I start fixing. But I'm thinkng of removing the inner panel where the moisture gets so it stays open, the rust is right where the spot welds are. Maybe that's knocking the rust treatment off from the get go.
Mike
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There’s panels available along with whole box sides. The problem with these trucks is where the inner wheel well meets the outer box panel, it creates a cavity on the inside. There are drain holes but they’re up about an inch or two above the seam where the two panels meet and it leaves a nice space for mud/salt to collect and rust from the inside out. If Dodge had put these drain holes at the bottom where the panels met it wouldn’t accumulate mud and rust out. The trucks that come with the plastic wheel well liners (it was an option) don’t seem to rust out (as it keeps mud and water from clinging up into this area). If you pull the tail lights out you can stick a wash wand right in there and clean the cavity out (but it’s a pain to do everything you wash the truck)

You can reach that area from the bottom, I use a garden hose with the end cut off (no brass end to scratch everything) and shove it up in there a few times a year. The liners do help but even in the last few years I have seen a number of trucks with them still starting to show rust through.

I tried to clean under there a couple times a year but it still bubbled on the drivers side. I had it repaired at a body shop and a while later it started to bubble in another spot. I sprayed Fluid Film (lowes sells it) everywhere I could get it under and between the panels. Then I bought Mopar fender flares like these:
https://www.amazon.com/MOPAR-DODGE-TRUCK-WHEEL-FLARE/dp/B00407OG9A
It gives a factory look and hopefully will hold up until the truck is junk or sold. I spray the fluid film once a year.