In eastern ND there is a county campground around Larimore. Around Devils Lake are some state parks. Fort Peck dam has several COE campgrounds. Havre, MT has a RV Park on the east side of town nest to the train tracks plus on in the fairgrounds on the west side. Fresno Dam/Lake west off hiway 2 has a campground.
Near the west entrance to Glacier Park has a bunch of full service campgrounds. We've always stayed at the Apgar campground inside the west entrance. They have water faucets and dump station along with restrooms in each loop.