So far in 2017 I have received the following discounts (from the actual rate the park is charging, not the rates listed on the discount group sites).
Good Sam Parks - 10 nights - $320.09 paid, $58.92 savings
Escapees Parks - 3 nights - $61.14 paid, $13.50 savings
Passport America - 10 nights - $220.00 paid, $126.00 savings
Federal Senior Pass - 90 nights - $1,209.44 paid, $1,137.06 savings
US Military Base Campgrounds - 14 nights - $312.00 paid (no 'savings' from the normal park rate, but all four visits were at places where the going rate for similar parks was $40-60 per night)
We are full-timers and have towed the trailer 11,018.1 miles so far this year, from California to Texas to California to Washington to Glacier to Yellowstone to Texas - 326 nights as of last night.
We stayed 174 nights in Thousand Trails campgrounds - for which we have a membership - at a total cost (including yearly membership dues, one 28 day stay, and 50 amp utility fees) of $997.43. "Free camping" isn't free - but it is very cheap is you use it - $5.73 per night avg.
Personally - we joined and are lifetime members of Good Sam because of the Good Sam groups we camp with, the state rally's we attend, the fellowship and other benefits. The savings on RV parks is a minimal benefit, but nice when stopping at a park while traveling.
We are members of Escapees for similar reasons, and our mail service and domicile/ legal residence is at the Escapees HQ in Livingston, TX.
Good Sam, Escapees, AAA, AARP, Passport America all are for discounts while traveling. Seldom do they work for a destination campground.