finding rv parks and rv resorts

In my experience no one directory or website lists all the campgrounds/RV parks. I use the following websites to find campgrounds along our route and still encounter ones that are not listed anywhere that I can find. Some of these websites have data sets that can be downloaded to a GPS or mapping program so that you can see whats available along your planned route. There are also many data sets available on the Discovery Owner's Forum and POI Factory.

RV Park Reviews
Passport America
Allstays
RV Parky
Woodalls
Free Campgrounds
Free Campsites
U.S. Campgrounds
National Forest Campground Guide
Ultimate Public Campground Project
Corps of Engineers Campgrounds