Iceburgh - not much to protect on your car with a bra!
BTW, that's the first really close up I have seen of your car.... and all I can say is WOW what a beauty. Should be hard to spot it at the local shows.

I ran a standard bra on my 34 (grill shell and both front fenders) for several years with no problems of abrasion. Of course the paint wasn't new to begin with, nor was it a trophy quality paint job either. I did remove the bra everytime after it got wet, since leaving it on wet will fade the paint. 99% of the grit was in the creases at the lower edge of the bra, not in the bra flannel it self.

Last year after an accident I had the front end re-sprayed, so now I only use the bra for long trips or under conditions when chipping might occur. While the paint was curing I didn't use it at all. You do have to be careful with them.