concept is good, I like it. however remember about that some of people don't want SS named "SS-something". Propaganda halftruck is nice idea, but it would fit to soviets better... nahh, who cares, Germany was also totalitarian, so it fits too ;D
Propaganda halftrack with loudspeakers were vastly used in the Eastern front during the siege of Leningrad and Stalingrad to demoralize the Soviet troops.