I found this video of using a sun roof visor for a window drip cap. Since the classic E-21 body has the rear side windows inset I don't think it will fit on a classic E-21. It looks like it may fit on the newer flat side body style trailers. The smaller sunroof visors are about 33" wide.
Since I own a classic I did not order one but I thought I would pass on the info. on this mod. for others with the newer flat side body style to evaluate. On the classic it looks like it will fit under the stowed awning rail not sure about the newer body style manual awning leg. It really may be more useful on the drivers side rear window. Just passing on information.
Eddie