Since you don't mind a little extra travel, the highlights of the UP are going to be Mackinaw Island, Sault St. Marie and then all the way down the coast of Lake Michigan from Petoskey to New Buffalo. I like to use the website www.rvparky.com to look at the camping options as you plan your travels. It's available as a phone app as well in case you change your mind along the way. We traveled in a 40' RV with a full size extended van as a towed and we had no issues getting in or out of the campsites that were listed as big rig friendly.
Have a great trip!