I have a full set of Fox and like the ride. I don't know what you'll actually notice just changing rears unless your current shocks are completely smoked.
They won't give you a new transmission, they'll top it off and say it's good to go. You can try to get someone to come out when you arrive and check the level with them so now they can't say "it was fine when we pulled it in"
Add the factory inside fender liners too so the wheel well doesn't get sandblasted. I take mine down one a year to clean up there and spray fluid film.
I've driven a customers Jeep that the front driveshaft u joint was so frozen up the whole thing shook like crazy. Make sure to actually take down the shafts to check, not just for looseness.
I see where you're coming from but frames are boxed now a days so unless it's done in a pristine environment and can't be fully submerged then moisture is likely going to be locked in. The backside of a panel is exposed so it can also dry. Also panels are typically treated in some way in a decent environment or dipped into some type of anti corrosive coating. Nothings perfect and it's all point of view or opinion.