Yeah, sometimes my router locks up, blocking access to my web page. It's back up if you want to try again.

Anyhow, since I was building a box with two seperate, sealed chambers, I used a solid piece of MDF running straight down the middle, from top to bottom as my starting point. I cut one edge so it lined up nicely inside the door, effectively splitting it in half. Then I built an MDF "frame" that went around the circumference of the outer edges of the door, and a flat board that the amp would later mount on. Once this rough frame was built, I stapled felt around the edges, creating a surface to lay my fiberglass on. It's probably hard to imagine what I'm talking about without seeing it... unfortunately I didn't take any pictures, but if you really are interested in duplicating the design, I'll try to explain it a little bit better and in more detail.

I also considered not using fiberglass at all -- the door would probably accept an "octogon" shaped sealed MDF box with a slanted front, and with this design you should probably not have much trouble squeezing 1.375 cu ft out of it.