Rust! Should I sell it?

Keep it. You may not find another.
So far I've gotten 5 years out of using multiple coats of rust desolver, sanding and wirewheeling until it quit turning white between coats then spraying rust reformer in hard to reach areas to finally top off with roll on truck bed liner to seal it. I did the whole trunk,engine bay,floor pan and undercarrige and have only had to touch up a few spots after 5 years.
Mine is just a daily driver.
Don't plug up or filler the hole in the rear quarter and make sure the drain holes between the inner and outer are draining properly, if plugged they'll trap water and will cause more rust if you plug it.
I've also gotten 10+ years out of using fiberglass filler on 2-4 inch rust hole after grinding out ALL of the rust back to good metal then using multiple applications of the rust disolver before cleaning extreemly well and glassing it.

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