US 12 North Dakota and Montana

Great thanks.

It's flat - the Montana mountains are along I15.

Two lane of course but not bad. I tow a 34 ft fiver over the stretch from Baker, Mt to Miles City a couple of times a year. There is an rv park just over the interstate as 12 goes into Miles City that we use. Not fancy but you get treated well and even though it is close to the interstate it is fairly quiet.

You might try Mile by Mile.

google maps tells a lot.