I stayed at Bear Paw campground along lake Itasca 2 weeks ago. Most of the sites are larger RV friendly but not all. Check when making the reservation.The bike/walking trail goes all the way to the headwaters and is excellent. I rode down on a Saturday morning at 8:00 and was the only one there. The fog was rising from the water as the sun came over the trees. We went back in the afternoon and there were so many people that there wasn't much point in taking any pics. The sun sets on the lake were beautiful.
The visitors center at the headwaters is very interesting.
I came across from the Straights and had also stayed at Bond Falls Flowage. It has limited big rig sites. I dont know much more about that area but I had seen the dirty end of the Miss so I wanted to see the crystal clear end. From there I went to the Badlands and Black hills