3 Hours would put you right around Wisconsin Dells, which has lots of places to camp. Devils Lake is the most popular state park in Wisconsin, and could be a great stop. There is also Mirror Lake, Rocky Arbor, and Buckhorn State Parks in that same general area. These parks do fill up quickly, though, so you'll probably want to make reservations.

If you're looking for a more resort style experience, there are also several RV campground/resorts with pools, water slides, mini-golf, etc. in the Dells area.