I've been a PPA member since I started full timing 4 years ago. It is a very good deal and you can recoup your investment with just a few stays. Most CGs seem to put restrictions on when the discount can be used but being a full timer makes this pretty easy to deal with.
I do recommend that you also visit rvparkreviews.com to see what kind of ratings your chosen CG gets.
Also, if you are at least 62, grab the Government issued lifetime senior pass for $10 now before it goes up to $80 sometime later this year.
I also belong to Escapees ($40/yr). They have about 15 parks scattered around the western and southern parts of the country where you can stay for about $20/nite. They also have a book full of private parks that have signed up to give 10-15 percent discounts to members. My favorite Escapees park is Park Sierra, located about 15 miles outside of Yosemite Park - parksierra.net