soon ill have mine up same idea (same spot) but ill be using a microATX :) it just barely fits, but my biggest problem is creating a venting system :/ esp since i live in an area were summers are very hot. im also able to use full slots.
If the op is still around I would like to know how he managed to create a vent systemů or do you even cover or place back the mats? Or did you cut a hole in those as well? If so what about when you have luggage or say groceries heh