how Did i miss this thread. after reading up I have some Ideas.
Windrock makes for a great home base style park due to the large campground, proximity to stores, variety of trails, variety of camping from cabins to tents at the campground and large staging areas.
To get the Multi Day convoy going i would suggest starting 4 small events.
Socal/southwestern group
Nocal/PNW group
northeast group
Southeast group
as each group starts off the trip they pick up more members as the progress toward the final destination. Doing it this way lets you plan the event anywhere in the country and people in every regions should be able to participate for at least one day if not make the whole trip.
I wouldnt be opposed to ending up in Colorado, Arizona, Oregon, Washington, hell anywhere is good with me.
However...
With a park like windrock you can make the event more like a jamboree feel. Large social gathering that has scheduled trail rides led by locals familiar with trails. Multiple departure times, multiple events throughout the day, group pot luck dinner, raffles etc...
If you try to do a trek style event the trip becomes more about the trip, If you do a Jamboree style event the trip becomes more about the lifestyle i.e. a car club meet with activities involving the cars.