Very Cool. I wish the rigid insulation was available more readily in the box stores around here. Its more than a chore to find a source and arrange for shipping.
I did something very similar but used 6 inch deep frames filled with R19 insulation\
http://members.toast.net/dwyss/pics/Room1.jpg http://members.toast.net/dwyss/pics/Room2.jpg http://members.toast.net/dwyss/pics/Room3.jpg