Get a car windshield cover of the type that uses a spring steel loop
covered with silvered nylon. Be sure to get the type that has two
separate hoops, and not two that are attached.

You fold these by twisting the loop and it shrinks down in size to
about a dinner plate.

Put this on the inside of the canopy using the springiness to press
against the plexi just above the canopy rail. Position the front just
above the instruments and the rear will be near where your face would
be.

I've found this covers enough to keep things cool, and in my forward
hinged canopy, it even stays put with it open while a breeze blows
through. When folded, it fits neatly in the top of my baggage
compartment.

-Tom