Not sure about the East Coast, but in the Midwest, there are not a lot of Passport America campsites. But those that do have pretty good discounts.
My Aunt and Uncle are full time RV'ers and travel in their Class A all over the country. They swear by Passport America.
You can download a Passport America iPhone/Android app that provides a search listing of the campsites by area. This is probably the best way to see what member campgrounds are located in the areas you want to visit.
I am a member of Good Sams Club, but mostly due to the Samboree and local Chapter aspects of camping together with other folks. I have not done a lot of discount camping with Good Sams (maybe twice last year).
The only thing that works on a RV is the owner...