With occupancy rates generally higher than 90% Disney really doesn't need to offer discounts to get folks to camp at Fort Wilderness. Discounts are generally used to increase occupancy rates of slower properties and/or slower times of the year.
While AAA discounts on sites are available for certain time periods, the number of sites is limited. You can book a site, and if AAA discounts are made available for the time period you are there you can call back and have the discount applied to your existing reservation.