Matt offered some very good Michigan sights as well as northern Indiana. Shipshewana is definitely a center for Amish activities, but there are a lot of crafty type places there too with the usual tourist stuff. For camping in Shipshewana check out the link below. There is a huge flea market there every Tuesday & Wednesday 8-5. It's lot of the same stuff, but there are some interesting things. Wednesdays at 9 a.m. is an auction that brings in many Amish.
http://www.rvparkreviews.com/regions/Indiana/Shipshewana.htmlIf on your way back south you stray into Ohio you may want to visit Holmes County. There is a nice campground in Berlin that we stayed at while visiting, Scenic Hills. This area of Ohio has the largest population of Amish in the U.S. Do some research before going so you can see as much as possible while there.
http://www.scenichillsrvpark.com/or you might like this one.
http://www.berlinrvpark.com/In Michigan I also suggest sticking to the Lake Michigan shoreline. The state parks are usually quite full during the summer though, but check them out anyway as you may find a day or two during the mid-week. State park reservation site below. There are also plenty of private parks along the way too. I'll offer a couple of suggestions below.
https://www.midnrreservations.com/Silver Lake dunes area.
http://www.silvercreekrv.com/Sleeping Bear Dunes National Lakeshore area.
http://www.rvparkreviews.com/regions/Michigan/Empire.htmlIn the U.P. we have stayed at Brimley State Park several times and will be there again in July. It has a nice beach and grassy campsites. It's also not far from Sault Ste Marie (called "The Soo" by Yoopers).
Another area worth visiting in the U.P. is Grand Marais/Munising. There's a nice little campground in Grand Marais called Woodland Park where you can walk into the small downtown area. It's right on Lake Superior with a very nice beach loaded with agates. They do not take reservations and when we were there a couple of July's ago we had no problem getting a site. Weekend can be more difficult.
http://www.rvparkreviews.com/regions/Michigan/Grand_Marais.html For Munising (take county road H-58 from Grand Marais) and the Pictured Rocks National Lakeshore check out this link for camping. There are lots of waterfalls in the Munising area and the Pictured Rocks boat tour is a must if you want to see the rock formations.
http://www.rvparkreviews.com/regions/Michigan/Munising.html