I use a computer program, MS Streets & Trips, you could use Mapquest, Google Maps, etc. There are several trip routing websites and abs that can show you campgrounds near the route you choose.
I also rely on OvernightRVParking, the website and ap to find places that are free or nearly so. And both RVParky and AllStays aps. Enjoy your trip!
May the trails always twist in your favor
May the tales always end in good light
May you have more friends than one campfire can hold