There are all kinds of discounts available to RV travelers. Each should tailor their accumulation of such discounts to their particular traveling needs.
When we purchased our fifth wheel and started our full time trek on the road, the dealer/company we purchased our fiver from provided a few starter discounts cards. Passport America was among them. We used it twice during the first year but never renewed our membership. We were travel in season and passport America is mostly valid at each seasons start or end. Thousand Trails was another but we never used it.
We joined KOA because we stopped at them a lot when on a long run. As time moved on, KOA started giving military discounts equal to their membership discounts (10% - 15%). I’m retired military so I quit renewing our KOA membership.
A very high percentage of RV Parks/CGs give some sort of discounts. About the only ones we have constantly been a member of is Good Sam/presidents club - now Camping World. Others are AARP, AAA and seniors discounts. Those are the ones most often used by us.
As someone has also mentioned, the National Parks card is a one time $10.00 expense and is our highest valued card. Some state parks and the Corps of Engineers will also honor it.
Always ask. Once in ND to visit the Theodore Roosevelt National Park our RV park gave two days free for every seven we stayed with them just because we were visiting the NP. When we asked them about discounts they told us of their policy for pricing for their NP visitors.