A little over 100 miles east of Chicago is Elkhart, IN, the origin of many RVs. Here's a link to RV salvage yards, a number of them in Elkhart.
RV Surplus And Salvage Used RV Parts RV Equipment RV Supplies RV Repair
I lived there a couple of years in the late '60s and spent a couple of summers driving a 'Roach Coach' to the various suppliers and builders of RVs, mobile homes, and trailers. I'd go from steel and aluminum rolling mills to window/door manufacturers to lumber yards, frame and axle plants, to assembly lines building the finished product. You can get about anything you need in Elkhart, Nappanee, Warsaw IN area.