Hi, I had the same problem in that situation. I have the exterior shades that snap in place, although mine use the velcro fastners. I went the Home depot and bought a couple of rolls of the foil and foam insulation - it is only about 1/8 inch thick with foil on both sides and foam in the middle. I tried just cutting it and placing on the inside but could not get it to stay in place for any length of time. Sooo I took my exterior shades and some new rolls of foam to a local business that makes boat canvasas and had him sew the insulation to the back side of the exterior shades. It made an unbelievable difference. I can even turn my front ac off at times. Most anyone with a big sewing machine could do it. Nothing fancy, just stitched all the way around one time. Hope this helps. It sure worked for me.
