Most CrewCabs are 7' wide... plus mirrors.If the space is 20 x 20, why cant they be parked side by side ?
Most trailers 8' wide.
Leaving 5 feet for 3 aisles, 20 inches between units.
Plus CrewCabs are at least of 20' long.
And an 18' trailer has a 4' hitch.
The guys organizing the events pick their target market and run the event accordingly.
I don't regard a 5th wheel or Prevost Bus towing a 24' Tow/Jeep Hauler an overlander.
There are plenty of events for bigger units.