OK, you are just looking at possible alternatives, so I will give you another to think about. I will just start at you Apostle's Island stop.
You may have a very good reason to stopover at Jamestown, ND, but on a trip east from T. Roosevelt we enjoyed staying at Country Campground in Detroit Lakes, MN. We would definitely go back there. It would be 288 miles from your Apostle's Island stop.
We spent a delightful couple of nights and days at Bismark/Mandan ND at the Fort Lincoln State Park. There are several Lewis and Clark sites to visit within easy driving. It would be 254 miles from Detroit Lakes.
It would then be an easy 135 mile trip to Medora and Theodore Roosevelt National Park. This short drive would allow you an extra afternoon in the park so you might not stay as long.
You need a stop between R. Roosevelt and Glacier. Our choice was to drop down to Big Timber, MT to stay at the Spring Creek RV park--right on the river. Very nice place for one or two nights. This would be 365 miles from Roosevelt.
From Big Timber it wouild be about 395 to the WESTERN Glacier Park area--less to the EASTERN. We stayed on the West at Hungry Horse at the Mountain Meadow RV Park. Definitely would go back there.
OK, these are just ideas. I enjoy the trip planning almost as much as making the trip, so I always like to see some of the alternatives.