I use this
campground map to find places along our travel paths. Shows both private and public CG's. Click on the camping icons and you'll find a link back here to do a search on that particular CG (sometimes I have to modify the search parameters to get more hits). If available, there's a link to the CG website and in some cases, a link to RV Park Reviews. You can also get a Google search by clicking on the link. All-in-all, this map gives a good first pass on what might be available in an area you're looking to spend a night.