Back in '68 when riots were going on everywhere, I was driving a beat-up old 1958 Chevy pickup, which was my "desert" vehicle as well as daily transportation. I never had a "truck gun" per se, but I would often travel with this baby parked in the rack in full view of the rear window. It gave me a certain feeling of comfort when I had to drive through some particular areas in Phoenix. I never left it unattended for any length of time.
John