The closest one I know of to Ann Arbor is the Detroit Greenfield RV Park (a few years ago it used to be a KOA). We've stayed there a few times: Its an ok park out-of-the way. A good place to stay if you need to visit the Detroit/Ann Arbor area with some stuff to do in the park.
Here is the RV Park Reviews entry on it: Detroit Greenfield RV Park - Ypsilanti, MI - RV Park Reviews
Here is the website for it: Detroit Greenfield RV Park
That will get you, probably, a good 25 minutes from U of M's library.
The next closest decent parks would be some state park campgrounds but you'd be approaching a 45 minute drive or more..