I'll have to go and do some photo research on this, but I'm not sure there is anything to be gained by wearing a zeltbahn over an early smock, the reason being that the smock is itself showerproof. It is made of the same close woven cotton duck that the zeltbahn is. I can't remember if the zeltbahn is rubberised, but since it was often cut up to make custom camouflaged garments, I'd guess not. In which case both garments achieve a measure of waterproofing in the same way, the close weave of the fabric is tighter than the surface tension of water (hence "duck"), the water rolls off. Of course a woollen tunic or pea pattern camo jacket has no inherent waterproofing of it's own (particularly the latter), so it would be worth doing. I suppose it could be done for additional warmth. There are plenty of photos of SS soldiers wearing their smocks over their greatcoats, but I'd guess this would again be because the greatcoat wasn't waterproof, just heavy wool, so in heavy rain would wick up the moisture until it was saturated.
Having said all that, they are exceptionally nice figures. I wonder what the prices would be like for 1/35th?
Edit - I have had a chance to flick through some of my Waffen SS pictorial volumes - "Wenn Alle Bruder Schweigen", "The Waffen SS at War" and "Waffen SS - A Photographic History". There was not a single photograph in any of these publications of a zeltbahn being worn over a smock. This is not to say it never happened of course. What is common is the smock worn over the greatcoat as in the second figure and, strangely, the smock worn over the Camouflaged Drill Uniform (often called the Mod 43, 44 or Pea Pattern clothing). In this case only the collar of the drill uniform is visible. This gives the nice mix of camo patterns.
"Lord Raglan wishes the cavalry to advance rapidly to the front, follow the enemy, and try to prevent the enemy carrying away the guns. Troops of Horse Artillery may accompany. French cavalry is on your left. Immediate. Airey."