In 2004, I organized , and set up the first rally, for an owners group in the SE.
Hanna Park in Jacksonville is worth investigating. Not far from I-10 and I-95. That makes it convenient to lots of east coast people. Lots to do on site or nearby.
COJ.net - Kathryn Abbey Hanna Park
They were willing to block off a group of sites for a period of time. That allowed me time to advertise the event. Plus they have common areas you can reserve for different events.
This is April. I would shoot for a September date. Somewhat off season plus gives you time to drum up interest.
Take a look.
Be sure to check for date conflicts with other competing events.