When you say designing, do you mean fabricating and producing your own panel, or airbrushing on an existing companies panel?
I am the last person on earth to give graphics advice, so I am unable to give you any ideas, but, I will say, if it had a bit more red in it, I would seriously consider one for my Torch Red Stang.
I think it looks really really cool the way it is now, just my personal preference would be to see the "Never & 9-11-2001 on the left with a bit more red in it to match MY car.
I'd be proud to fly that panel on my car, KUDOS to YOU for what you are trying to do here, I commend you and wish you the very best of luck.
Now the stupid question, that website info would not actually be on the panel would it? I assume not, but thought I'd ask.