I've liked the look of these for a while:
http://rawmudflap.uk/
Well, I was going to butcher some butyl pond liner, but now I'm considering both the rawmudflap and topflaps suggestions. Particularly liking the raw reflective stealth design. Thanks to everyone!
I have the retro-refecltive
RAW on my CGR, bought whilst it was on order, so been on it since 'day 1'
Normal
Caught in lights (flash for this image)
Both F + R are reflective
Now, there's an extra reflector on the flap
With hindsight, that was a mistake, as on steep hills, if out of saddle, it 'slaps' against the tyre, with the added weight of the reflector (circa 2inch x 1 inch)