Wishin,
A couple of things to keep in mind. Montana is the 4th largest state in size and 44th in population. If you get off the interstates, you'll be passing through small towns that may have only one gas station and your rig might not fit. On my trip to Alaska, I stayed on I-15 N from Great Falls to Sweetgrass, MT. and still nearly ran out of gas trying to find a station with pull thru pumps since I tow a Jeep 4 down and can't back up. There's a gas station at the border into Canada that was Very busy.
Second, the Badlands loop road is only 40 miles long. Certainly worth a drive through. Several turnouts to pull over and walk around. I stopped at the gift shop on the way out. They have shaded benches next to the door. Also a sign warning folks to look under the bench before sitting down. Rattlesnakes like the shade during the day. I don't know if they were just joking, but I looked first.
