Well, that's not a worst case by far, but uglier than I had hoped. At least there still isn't much rust.
I knew I had some DIY-ish repairs going on in the quarters.....I estimate that I removed at LEAST 2 gallons of kitty hair and mud from the passenger side quarter panel. After a couple smacks with my fist, a large pucker that was full of mud popped out.
I will still need to replace the wheel well lip and the butchered lower rear section at a minimum. Access from the inside would sure make things easier, but I'm hoping not to have to go there.