Well in that case, I would sketch out a general route. Google's bike route directions returns a 152 mile route from Champin to Duluth that incoporates some trails. Then I would use the search methodology I decsribed above, picking towns that are along the preliminary route and that are within range of your expected daily mileage. The route Google returns goes through Moose Lake, where there just so happens to be a state park with a campground. There are a couple of places along Rush Lake, which is a few miles off route.

If you ask Google for the route and then pick a town and search for "camgrounds near [name of town]" the campgrounds willl be shown and the lines showing the route will remain so you can easily see the locations of campgrounds in relation to the route. BTW...The route Google returns goes right in front of the Hinkley Fire Museum. Banning S.P., which has camping, is about 8 miles north, just slightly off route.