There may be some camping available in Teddy Roosevelt NP, not sure though due to the activity in nearby Bakken Oil Field. Check wth the Park Service folks as to availability. Think there is a CG at Fort Union which is on the MT/ND border at the confluence of the Yellowstone River with the Missouri. Just a few miles away from US 2 if I remember correctly. There may be a CG near Mandan ND, but not sure. However the Mandan area is definitely worth a visit to experience the Lewis & Clark expedition of over 200 years ago.