Numerous campgrounds that are primitive. They let you park your rig so you can go select a site in the rustic camps if you don't have a reservation. We didn't and it was fine. However the park is vast so have a few picked out when you get back as it may be gone. Bring lots of OFF & a screened in tent for some peace.
Lake in the Clouds is the most beautiful spot in all of MI. Be sure to see the waterfall. It takes 40 mins to drive across the park, but worth it.