Tumble,
Lowes or Home Depot has Lexan in sheets big enough for the door. I did mine by taking the door off and placing it's front onto the sheet with the coating side up. Took a magic marker and traced around the door and cut with a jig saw. Used short sheet metal screws with large heads to attach after pre drilling holes in Lexan and frame of door. Make sure to make holes in Lexan a little larger so that it can expand a little. Do not try this with cheep plastic as it will crack and break. You will also have to cut out a small place for the latch. If some pictures will help, let me know.
Ken