The name "Heideperle" shown on the original pic could indicate that it's built near the Lüneburger Heide. I vaguely can spot a coachworking company starting with a "W" and maybe 5 or 6 characters.
I found a still existing truck coachbuilder called "Wille", resident in Lüneburg which is in business since 1895.
Not that likely, but could it be them?