We made a coast to coast trip last year, Massachusetts to California and like you we used the National Parks to guide our travels. The Iron Butt Association has a National Park Tour certificate, if you are so inclined. >>>
http://www.ironbutt.com/themerides/npt/
Essentially the NPT is capture 50 parks, memorials, battlefields, in 25 states using the cancellation stamps
Good luck and have a blast and safe trip
Willie