In the southern half of Wisconsin, you will be hard pressed to find anything which is a suitable (or sanctioned) "forest" boondock. In addition, the western, unglaciated part of southern Wisconsin (from Baraboo south to Illinois and west to Iowa and Minnesota) is, IMO, much prettier than the eastern half. If I were you, I would especially stay away from Milwaukee, really anything along the western shore of Lake Michigan until you get well north of Milwaukee.
If you were to drive from Amana, Ia, to Prairie Du Chien, Wi, you can take the
Great River Road (which is surely one of the most beautiful drives in the US east of the Rockies) north to La Crosse, Wi, and then start north through Eau Claire to Trego, Wi. North of Trego, you would follow 63, which runs along the
Saint Croix National Scenic Riverway which offers some nice places to camp, then to Ashland Wi, then east on 2 to the UP, or Hayward Wi, then east on 77 to 13 to Ironwood. Either route will take you through the Chequamegon NF, also offering some nice places to see and camp.
Another option would be to take 151 N/E through Madison, then on up past Appleton and Green Bay and then through Marinette, and then 35 which runs up the western shore of Lake Michigan, and then choose a path north to the southern shore of Superior.
If you were to travel as far east in the UP as possible, you would get to
Drummond Island which is now Lake Huron. Which is pretty cool, too.
