If you stay in Mackinaw City, Rainbow Motel is a nice, clean and family owned. Lots of riders stay there, and you park right in front of your room. From Mack City follow C66 to Cross Village and stop at Legg's Inn, a must see, follow M 119 ( Tunnel of Tree's) to Harbor Springs, nice place to stop and shop.
Depending on how much time you have, you could follow 119 down to M31 and take to Traverse City and then follow M22 to Northport and on down to Manistee and Ludington. Lots of places to stop and shop on M22. If I remember right, gas and places to stay on 22 are scarce untill you get back down to 31 around Manistee and Ludington.
I remember reading about a campground very close to the Mackinaw Bridge in Mackinaw City.