Dave did a video talking about the no prep thing. One thing he mentioned it that per the no prep rules the cars must have metal roofs and quarters as well as a VIN. He said that Birdman and a couple others had fiberglass cars with metal panels attached to the roof and quarters and a junk yard VIN tag. That was part of the reason he didn't race in the series.
James
https://www.youtube.com/watch?v=HZSnQEkGIaE