See these here vent assemblies? depending on car and year,they can weigh anywhere between 4-7 lbs for each side. Here is a 65' unit weighing in at 5Lbs that I plan to look at just a bit, bit closer.
I already know since it has been changed to Lexan way, way back that the glass itself is a hefty piece, but it is in the tracks and cross braces where the real sneaky weight lies dormant. Let's knock on the door soon.
This will be fun in finding both time and the material to construct a new feather vent.