Thanks for the input, Fifty150. I did plenty of that car-camping, but I bought this van specifically to make it a comfortable place for longer road trips. My idea is to make the setup and tear-down of camp as quick and easy as possible. I totally respect the minimalist approach, though!
Webguyjv, I'm right there with you. I'm not planning anything "permanent", but I more mean that I'm not planning anything irreversible at this stage (i.e., not cutting any holes in the roof for a fan just yet). I might go the hole-in-the-roof approach someday, but that's definitely a more permanent approach. For now, I'm likely going to just fashion some bug screens and use a couple clip-on battery or 12v fans on the rear passenger windows.
I think I'm going to go with my original idea of a simple drawer system bolted in where the third row seats were. It will be easy enough to unbolt if I sell the van and don't want to sell it private-party as a camper. Something like this: https://www.contravans.com/5-passenger-van-conversion
On a fun note, my 12v fridge just arrived and the battery is on the way ?