If it's not completely opaque, you may end up spending a lot of time working to obscure the base vehicle. May not sound so important, but if you don't obscure it enough they'll give you a big fat no, and all those months (and dollars) you put into it will be for naught (well, it'll make a great decoration at camp…). Actually, from my own experience, even with completely opaque fabric you'll still struggle with that. Bring more fabric than you think you'll need.
A flammability test is a good idea too (some of the stretchy stuff burns easily and quickly), and plan to pack a couple extra fire extinguishers for the vehicle. You'll also want to make sure you don't find yourself too close to any of the burns (floating ash/embers), and make sure your drivers and other crew members know where the extinguishers are and to keep an eye out for embers as well as passenger cigarette burns.
Depending on the weather, you may still end up having problems with the wind. When I did a fabric covered vehicle in 2007, we used breathable fabric and it was attached to a steel frame - the wind was severe enough that the fabric + wind bent the frame in a few places. Make sure you bring the tools you need to be able to repair/recover from whatever the playa throws at you.