Temporary cardboard partial Kammback

I have been planning the permanent version for a while but I decided to do this temporary extension to see how it effects rear visibility. It only took about 30 minutes to make and it didn't look too bad when I first did it, next day there came a torrential downpour and I had to do some repairs to it so it's not quite as pretty now. I'm hoping to keep it on at least one full tank to see how much it improves FE. Since I've had it on a few days I think I will make the permanent version longer and incorporate a clear section in the center for visability, haven't decided on how to attach at the edges yet but I'm thinking either sheet metal or fiberglass to form the curved part while the center flat section will be lexan os something like that.