[slomotion]

The only caution I would throw out concerning the brackets is before they are permanent make sure they don't whistle going down the road. Don't know how your going to test them ahead of time though.
When I built small boats I used to deliver them on brackets fastened to the roof of my van. If I didn't get the boat just right on the brackets there would be a moaning sound start at about 50 MPH and it would get loud about 65. (Just like blowing across the top of a soda bottle.) All I had to do was tie a rag in a knot to the after bracket to disturb the air flow and it would go away.
Anyway, I said all that to suggest you fab your brackets with the idea in the back of your mind to have some method to disturb the air flow if they whistle. (Doesn't have to be a rag)