Seek and ye shall find. For example, a model of the Westfalia advertising train, albeit with a Ford FK 3500 (unfortunately it's already too late for the Christmas wish list).
Unlike the Phänomenon, it has no windows. So the loudspeaker was probably only there to attract and inform customers. The Phänomen had a small seating area in the rear. For customer meetings and/or for employees to stay. The rest of the superstructure was used to transport the material, possibly also partly for exhibition purposes.