Heres why the rear lower quarters rust out..

tonysrt said

You also have to remember that the tire picking up dirt and hauling it into the wheel wells is like a sandblaster eating away at the metal. If Chrysler used a little thicker metal in those area's maybe our wheel wells would have stood up better. And of course problem is worse in snow belt because they use salt or sand when it snows.

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That was my opinion as well, as you know rocks and crap fly up and chip the paint under there.
I'm having a hard time actually making myself do it, but after fixing those rusted quarters I am considering doing the rubberized coating under the paint on them.
You know, just along that bottom strip and about 2" up the sides.

Just not sure it would be worth seeing that on the panels though.:D