Yes, that's too many miles. Besides the driving time you have to check into each campground and get set up each night. Then in the morning you don't have to check out, but you do have to get ready to move.
If you're not planning on seeing anything on the way over or back, leave the MH at home and fly. Renting a car and a hotel room at Glacier NP will be cheaper and more relaxing.
Have you heard of the old 10-2-5 rule? On the road at 10:00AM, off the road at 2:00PM and a cold beverage in hand at 5:00PM. That's about 250 miles a day. You're going to try to double that every day and almost triple it one day.
Bill