The Fort offers limited AAA discounts. They only allow so many discounts so you may sometimes be told there are none left, but don't give up hope if they tell you that because you can still get them if someone cancels. (This is how we got one two years ago.). I kept calling every few weeks and happened to get lucky!. Sometimes they offer them to just specific type loops (full, preferred and/or premium).
This year I made our reservations in June and they were giving discounts for only the "preferred" sites, so I jumped on it. Also, like QCCowbow mentioned above, we have the Chase Visa card and use it like a debit card, putting everything we charge on it and then paying it off every month. We now have more than $500 in rewards to put towards the balance. It was a win-win for us.