I think it looks alright, but I wouldn't want one. It is too big, and sort of ruins the curves of the car. It sort of looks like you laid a board across the back.
The first picture looks good, the one's of the car on the road don't look good. I would make it a little smaller in length, and curve it more with the car. So instead of it coming off the car and doing a 90° bend, make it curve off the car, and then go across. This is just my opinion, which is what you said you are looking for.