About model:

The 3cm Flak 38/103 Jaboschreck was based on MK 103 aircraft cannon, it only went into production in small numbers before the end of the war.
Some picture shows this gun mounted in soft vehicles such Steyr Type 2000A, but we haven’t found any evidence of it mounted on an Opel Maultier, so this works is also a sort of “What If”, while quite possible.