G.B.
When I plan a road trip I go to each states tourism web site and order their catalogs. I see what is along the route we are driving and decide what to throw in the mix. We sit down and decide what we want to skip and what is a no miss attraction.
For instance, when we traveled to Billings Montana I had a trip plan months in advance that took us to museums, parks, animal reserves, train displays, national parks like Mt. Rushmore, etc.... I took all the information from the Nebraska travel book and Wyoming travel books for the going trip and for the coming home trip I used the South Dakota, Iowa, and Kansas tourist books. Just look up the states and get the brochures that look interesting to you and your trip will plan itself.