Sites at the Fort are hard to book almost ANY time these days,
@chindog. What dates are you currently looking for?
The Fort has the same number of RV/trailer/tent sites as it did in 1977-ish. In the mean time, the number of campers and rv'ers and Boomer Babies and all have skyrocketed in the intervening decades. Since the supply of campsites has stayed the same and the demand has grown, prices have shot up and booking a site is tough.
Used to be that you could book your arrival day up to 500 days in advance (for a max 30 day stay) but Disney is currently restricting that (500 days now goes into 2023 and 2023 arrivals are restricted and not available yet per Disney).
So it helps to book WELL in advance (a year during slack times) and at/around the 500 day mark for holidays, spring break, busy times (summer is suprisingly not busy other than July 4th week because it is so hot).
The other dynamic to be aware of is that folks near WDW ("locals") book weekends at the 500 day mark BECAUSE THEY CAN so often you can get weekdays (Sun-Thur nights available) but can't get Fri and Sat nights.
I don't like it - it's changed so much over the last 20 years I've been going to the Fort. But that's how you have to play the game if you want to book ahead.
The alternative is to select the level of site you want (if you are long then a Premium Meadow or Premium) and book what you can get in your time frame window. A day here, two days there. You can string them together and later get them combined into one reservation (same level and consecutive dates).
Disney doesn't make it easy. It is what it is. But that's what you need to know going forward.
Good luck!
Bama Ed