I note that no one has mentioned the Good Sam Trip Planner.
Since you are already a member, it is free. Go to the GS Club website, log in and open it. Take the tour. The learning curve is not steep and you can tailor trips to your liking with a little practice. Set waypoints and it gives you total miles and "link miles" then you can ask it to display CGs.
The end product is downloadable to Rand McNally GPS systems (and possibly others).
A
ON EDIT: After I have an end point for the day I go to RV Park Reviews (which I believe now calls itself CampgroundReviews.com) and Passport America to see what "other" CGs may be available.