Okay, you can go here http://forum.grasscity.com/photopost/showgallery.php?cat=500&ppuser=31591 to see my setup, and the cabinet I bought originally had a cardboard like material on the back. I easily took that off and replaced it with a like size of flashing. Now what I'm wondering..... Is flashing a good reflector?
I honestly don't know, but I doubt it. It's just stamped sheet metal, probably reflects hot spots. My advice is paint it white or cover in mylar.