My only concern would be actually getting the material to conform to the shape of the doors. The material would have to be very stretchy and you would have to find a glue with a very high initial tack to be able to grab the material and hold it. Five yards should do it though.
I did a 3-way speaker setup in my doors that seems similar to what you're planning. I'll post pics later (at work right now). I originally wanted to do material on the bottom, but couldn't find something that was stretchy enough, besides spandex. I don't need to explain why I didn't do that
So I opted for a textured black paint that actually looks
very OEM. I was happy with how the paint turned out, though I think I could have done a better job with the fiberglass.