This idea of yours brings to mind Col Hessler's mobile command post trailer that was towed by halftrack (I think) in the movie Battle of the Bulge (1965). I remember it being very workmanlike in construction and basically a rectangular box on 4 wheels. It had a door on the side with perhaps a steprail or folding steps under the door. No windows and the exterior probably had some rivet detail. Lightly armored but it did get blown up by a mine in the movie. It was painted gray to match the tanks.

Maybe someone can provide a screenshot from the movie showing this particular "caravan". I've always liked this movie but I don't have it in my library.

-Harq