I had one of those sandwiched between some wool Army blankets when I was in Germany. Used them to replace my sleeping bag. A lot less weight, water resistant and warm as anything.
Might have to construct something along those lines. But it sure would be nice to find one already made.
The one I had, until last month, had velcro on the sides and you could use it like a poncho.
I will get back to you in a few hours.