I haven't read all the posts, but wanted to share my experience.
I have 3 girls and they are very used to traveling in the back seat of my truck. In 2012, when they were 10, 13, and 14, we went to Yellowstone from Massachusetts with 2 other families that had 2 kids each. That's 2400 miles each way. We did have 21 days total, however, but MA is much further east than MI.
We took 5 driving days to get there. Stopped in the Black Hills on the way home. Everyone loved the trip and would do it again in a heart beat.
We loved it.
