We prefer the Blue Highways to the interstates other than around larger cities. We will have a few major destinations in mind when we head out. On travel days, we will go 200-250 miles (4-5 hrs) or less. I use a mapping program to find the general area where we will likely land at the end of a travel day. Using the mapping program and internet sites like RV Park Reviews, RV Parky, Allstays, Passport America, and the Ultimate Public Campgrounds Project; I compile a short list of 2-4 potential stops. About noon, I will call to check on availability. I will usually not rely on just pulling into a campground. Once we arrive; I will ask staff what there is to see and do in the area, look at any brochures they might have and do an internet search for things to do. We have on a couple of occasions stopped for a night and ended up staying a week.
I also use these websites to find attractions and places of interest:
National ParksNational Wildlife RefugesState ParksScenic BywaysLegends of AmericaRoadside AmericaGhost TownsSlot CanyonsFactory ToursNational Historic TrailsCivil War TrailsState Tourism Websites