Check both of those wing windows. They may be broken and not seal well. It's a weak spot on these B Body wagons.
Haven't been to a rodeo for a while, huh? I got some at the Calgary Stampede back when I lived there. Lost them over the years. I was just mentioning to my wife about the Brandon Rodeo this summer, and she wants to go. Next time we go to Leon, Guanajato, MX, I'll PM you their prices. The best leather boots and shoes, ANYWHERE! Over 200 worldwide brands and manufacturers. Better than distributor prices.
Is it the wheel well or the spare tire well that is rusted? If its where the spare goes taht seems to be a problem with all B-bodies. Also the undercoating and sound deadening stuff comes off from inside the wheel well behind the tire on B-Bodies. Just common problems. I have it on both of mine. BTW if you don't mind using a space saver spare you can take out the spare tire well. I did it on mine as it would drag going in and out of some lots even when it was stock height. I took it out and the wife welded in a new shelf. Now it looks better as well. BTW welcome to the site.