Consider single stage / urethane paint and hardener, hit it with that after the epoxy paint. Any color - lol. Clear coat with hardener would be fine also.
Then schutz.
More layers to keep out oxygen.
Im speaking from no scientific basis whatsoever.
Ohhh - Fluid Film over the Wurth/U-Pol stuff. Joking but would it hurt?
My 81 had road crud (and some rust) packed up in the front inner fender in a spot which may be where you speak of. I did the same routine you are doing.
I'm curious, is the problem area you talk of in the area of where the arrow is pointing? The corrosion was in the wheel well innards, not the outer panels.
