In my day job I was responsible for a motor vehicles. The solution of a trailer vs. a vehicle is idea for amateur radio and Emcomm. The motor vehicle is more expensive and requires regular operation and maintenance, not something volunteer groups are good at. It is much easier to have a collection of prime movers in private hands that can deploy the trailer as needed and retrieve it later. A group could get two trailers for the cost of one van. A local group has a surplus paramedic van, but it is old and when things break, they have to scrounge the money for repairs.
I also suggest that volunteers trick out their own trucks and cars as individual radio stations. These can be deployed even more readily than vans or trailers, can be parked to avoid desense problems, but still close enough to coordinate.