Without pictures, I can only assume they have something like the Eaton DC quickcharger and generator mounted to the trailer. These can bring an electric car from 0 to 80% charge in under 30 minutes. They are the equivalent of the CAA bringing stranded motorists a couple of gallons of fuel.
Using electric cars for cross country trips at this stage is like pounding nails with a screwdriver. Not that that has anything to do with how people would actually use an electric car, ie commuting and trips around town.