Hi
I've stopped at Romney Farm a few times now, lovely place. But last year i was the last person to leave around September 14th , they closed the site for a few months as that's when they take their holiday.
You could try Lords Farm, i haven't stopped there but it looks ok and I think it's open all year round. This year I stopped at Norwood Farm, lovely site but I think it closes on 1 October.
There's b& b at Pluto, Dungeness. quite reasonable rates. There's also a b and b somewhere along the Lydd on Sea drive which does birding weekends.
Lisa