wheel well rust

[gary_lucas]

ugh.

https://goo.gl/photos/1xzrNhHrYq4QuDzT6

Notice it's all buried under where the flashing and cover goes?

I'm sure this won't be the only time allot of people on this forum have seen this sort of thing. Until I took the whole shroud and mud flap off I couldn't see anything was wrong in the area.

What's the recommendation for avoiding this? Take it all off once a year and rinse and inspect? Is this common or did I get unlucky?

My plan at this point is to remove all the rust (I may bring it in for a sandblasting)... Primer it... Maybe some foam to fill the cavity after a couple coats of primer and paint... Then bondo / fiberglass and reinstall flashing etc...

I'll also be taking all the flashing off the other wheel wells to inspect in the near future. I know the rear wheel wells are going to suck. I thought the front's were ok

edit:
* I'll probably try to NOT reinstall the exterior plastic flashing. I think that's why my truck is rotting out. It just catches water