I have been thinking about this. If you are willing to go for a very basic shape with a flatish door and angled in upper door with window, you can buy a torn set of fabric doors. You would need to remove the fabric and place a fleece blanket all around and then pin or sew it into place. You would then use the chemical compounds that convert fleece into a solid for certain types of body work and fiberglass work. This would make a cheap, thin, strong door. You would reuse the door locks or replace the door locks with Jeep Wrangler type locks that are found on the Plan B doors. You could easily then cut in sliding windows. You could also easily slip in reinforcement steel or aluminum plates to support hinges and locking mechanism. Finally, use the JC Whitlessly door gasket material of your choice.
If you do not wish to invest in a bad set of cloth doors, I guess you could also bend up a 12 or 15 foot length of one quarter or 1/8 inch steel rod along the same pattern lines used on the cloth doors that you already own. Then weld the tips together where they meet. Then follow the same instructions.
This would allow you to make very basic but functional doors.
Best,
T