Nice little campground. We stayed two nights in Mandan #5. Positive is flush toilets and free hot showers with good pressure. Good potable water access. Also had very good cell service with T-Mobile phones. Mandan loop has the house with three showers.
Negatives: as others have mentioned, the traffic noise on the interstate is quite noticeable - we used a small portable white noise machine to help with that issue. Our site was not very level, but we were able to get our little pickup turned at an angle to level out our rooftop tent enough.
Biggest complaint is there seemed to be no evidence of a camp host, or any other person keeping the place maintained. Maybe that was over for the season, but we didn't see anyone, and the bathrooms and showers were not clean. No toilet paper, other than what seemed to be a roll or two donated by other campers. We stayed at another campground on this trip that had vault toilets that were cleaner, better stocked, and better smelling. Note - no lights inside the showers or toilet rooms, so take a headlamp or flashlight at night. Our site did not have a sign indicating that we had reserved it, only a plaque saying reservations are required.
Overall, an OK place to stay for a couple of nights, especially for hot showers. Easy access to Medora and Theo Roosevelt National Park. If showers are not vital, the Cottonwood Campground in the Park might be a better and quieter option.