We have stayed at Bayou Segnette many times, and it is a huge, very nice state park. Paved sites, as I recall. I would think it could very easily accommodate a rally.
We always drive to the Algiers Ferry, from the park, which is 10-15 minutes away. Ferry has been free, but Doug is thinking it may have recently been given over to a concessionaire, and drops you off in the French Quarter.
There is a private, monitored lot at the ferry, where you can park for $5 all day and $10 on weekends. Beats trying to find and having to pay for parking in the Quarter.
Some will say the Ferry is in a bad neighborhood, and that may be, but we are not afraid of this area in the daytime. Have never had any issues of any kind.
We always tell folks who want to enjoy the nightlife in NOLA to spend the big bucks for French Quarter RV park, which is a short cab ride back to your RV.