The event formally takes place from Dec 29 thru Jan 1. Some folk arrive several days earlier than the 29th. We went down on the 27th and there were close to 100 buses already parked when we arrived evening of the 27th.
It's a mega bus bash! You'll enjoy seeing the buses and meeting hundreds of bus'n folk. You'll be able to put faces on all these funny board handles!
Don't know where you are located, but there are smaller bus gatherings within easy driving distance of most places.
There are not many of the magnitude of Jack and Paula's Arcadia Bussin' event.
You may see FMCA rallys advertised, but generally they are more RV (S&S) oriented. There are exceptions and you could monitor FMCA's website for locations and event calendars.