I had a Bra for my BMW, and found out a few very important things:
1. Do not keep it on your car for extended periods of time, as the paint underneath will not match the rest of your car (fading and such). I would keep it on for two weeks, and take it off for one.
2. Make sure to clean it completely, as you can really scratch up your hood with debris embedded in the fabric edge.
3. Let it dry completely when cleaning. I found that taking it off, using some Dawn, and air drying for the night did the trick
4. If you want that nice new look, I would use some Vinlex (from the makers of Lexol). Very nice, keeps the shine, and keeps the grime off (it won't wear out the Bra).
I hope that this helps. I cannot stress enough how important it is to make sure that the inside is clean when putting the Bra back on your car (you might cry when you see all of the scratches . . . that you were trying to avoid in the first place).
Best regards.