Roadcamping.com is a free directory of RV Campgrounds in the US encompassing an impressive number of close to 8,000 campgrounds, half of which have detailed GPS and map directions attached to them.
When entering the site, users see a map of continental US divided by state, which then leads them to a directory of each state’s campground locations, listed by town and highway (state, interstate, national). When picking one campground, there is generally a brief description of its facilities, and a link to its site is provided when available. Campground owners are encouraged to submit their camps to the directory for free, and are requested to indicate their geocodes (latitude and longitude, that is) is order to be able to place all the campgrounds in GPS for one good reason: most campgrounds don’t have a traditional address and can therefore be a bit hard to locate, whereas having it laid down on a map is very convenient. 
