Top side, bit dusty!
Hopefully it will be fairly weatherproof. Canvas rectangle (the stuff car soft top roofs are made of), hemmed and with the press studs fitted was

it takes up no room when rolled up, better than trying to juggle the blimmin' great bit of plastic when you are out and about!

the central rear press stud is in the wrong place - its right above the handle area and there was not enough room to get the screw in very well.
I should have thought of that and had the press studs fitted either side - doh!