We bought two rolls of Aluminum Bubble Foil Insulation
at Camping World and cut them to fit our back windows and back side windows above the vents. I used 2 ft. wide yellow trace paper to place against the window and trace the outline with a pencil to make a template. Cut the tracing paper, recheck accuracy at window, lay over the foil and use a Sharpie pen to to mark the edges. Then cut the foil with scissors at the edge of the pen marks. The fit is so precise that it friction fits nicely but I think I will add some Velcro tabs. We won't cover them or finish them off as the OP did. The aluminum reflectance will help in sun and heat situations and they are strictly utilitarian and put up only if needed.
One 10 foot roll was good for the two rear windows and one side window. I needed another roll for the second side window (39" long) and may use the remainder for the windshield.
Now we are ready for the desert Southwest heat and Walmart overnights under the glaring lights.