I did this roadtrip after my ACL surgery when I was feeling sad that I couldn't do all the things I loved outdoors. Instead of taking those negative thoughts, I turned them into positives! I was able to see SO many beautiful places in 2.5 weeks, leaving from Seattle.
A couple places you can add in if you have the time:
-Craters of the Moon
-Badlands
-Stanley or Sawtooths, ID