Being that the bracket is so short, I do not think that it would make any significant difference being made of steel or aluminum.
If vibration becomes an issue, I would try using rubber washers or grommets.
If you go the rubber route, you will also need to use nylon lock nuts, as you do not want to crank down and completely compress the rubber.
If vibration becomes an issue, I would try using rubber washers or grommets.
If you go the rubber route, you will also need to use nylon lock nuts, as you do not want to crank down and completely compress the rubber.