Best way to see your country...and every single small town you roll thru will have a city park and I have yet to see one that forbids overnight parking. And there will be many small RV/camping places too, along the way.
Plus, big box store parking lots are readily avialable. If you are traveling the city park/big box route, you may want this...
http://www.sanidumps.com/September is such a great month to do the run. Lots of cattle movement to be seen as you move into the west. Get some prairie oysters here and there.
Gary Haupt