He attached them with 20mm spacers to the back end of the canopy to act as wind deflectors. These deflectors served the same purpose as those chrome flaps the old timers had on the back of their Cortina/Valiant station wagons. Hence we called them Cortina Flappies. Wind flows into the gap from the front as the vehicle moves forward, and then gets blown out the back across the back end of the canopy.
From the front:
And from the behind:
From a distance you can hardly notice them:
These things WORK! After driving 700km on very dusty roads the only dust on the back of the vehicle was a little bit that got stuck to the window rubber. The rear window, rear canopy door and even the tailgate was dust free. Okay not entirely, but almost..
If my logic is correct, the wind flow across the back of the vehicle also breaks the vacuum that gets created behind the vehicle, reducing the drag.. Where are the air-flow specialists? Could that be true?
I have a few more wind deflecting ideas up my sleeve. Let's see where this takes us.
PS They dont work so well with mud...
..... You wouldn't understand.... 
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It's as Cassie said .... it goes a long way to neutralising the turbulence behind the squared off back end, which is responsible for the dust deposits on the back. Dust from the wheels coming through under the vehicle as well as along the sides is sucked into the 'vacuum' behind and is trapped in the turbulence for a short time up against the back. With the 'deflectors' (side scoops sounds more accurate), the turbulence is less and occurs a little further back .... less dust deposit.
