As previously said, there are a lot of CGs in Michigan. You can download a Michigan Campground Association booklet or request that they mail you one at this website
http://www.michcampgrounds.com/
IMHO don't miss
trying a pastie,
blue moon ice cream,
digging your toes into the sands of Lake Michigan,
sampling the fudge at a good fudge shop where you watch them make it.
Cruise or kayak at the Pictured Rocks
Cruise through the Soo Locks or watch the Locks operate from the viewing platform.
Bike around Mackinac Island
Go into an iron ore mine in Hancock.
Search for Petosky stones on the lakeshore
Visit Sleeping Bear Dunes National Lakeshore.
Oh, I almost forgot. Sample the beers of Grand Rapids. Beer City, USA (shameless plug for my hometown)