Shade protection for the car

I always hate using roof bars on the car and have been putting off buying sheets of plywood, even though they would be useful, as I didn't fancy transporting them up form the valley.
As Tricia and I were driving along, each with a hand out of the window holding onto the sheets, I knew I had been right to put it off. We did eventually get them home intact, stopping regularly to add more bungees, rope and anything else we could lay our hands on.