I just wanted to share with you my oven door. I tested it a few days ago and it did very well. It is made from thin 1/4" cement board and 2" of the insulation blanket left over from the project.
I used fire silicone and fiberglass to glue the 2" thick cement box together after I filled it with the insulation. I sanded it down until it snugly fit in the ovens opening. I glued oven cord around the top and sides of the box to seal it against the brick. I made the decorative door from cypress and teak.