Agreed on spending some time in Wisconsin. They have some of the nicest state parks in the country (IMO), and some of them will have room for your rig. During the week you may be able to get a site evem without an advance reservation. Check into Governor Dodge or Devils Lake SPs - they are very popular, but if your trip isn't for a few weeks, schools will be starting and the parks will be less busy durin the week.
Effigy Mounds is a small national monument/park in northeast Iowa, dealing with ancient Indian culture, interesting place. We spent a few hours there once when camping in s.w. Wisconsin. In central Wisconsin there are not only all the tourist traps in/around Wisconsin Dells, you can visit the International Crane Foundation in Baraboo (dedicated to all the different birds of the crane family), Frank Lloyd Wright's home Taliesin in Spring Green, and The House on the Rock - not like any place you have ever seen before! You could base camp in the Dells or Baraboo (or at Devils Lake SP) and see all of the above (except Effigy Mounds) in short day trips.