At 10-12 times radius to the diameter you don't need any mandrel, sand or etc in most bends. Not even close to a problem. If you can find a conduit bender that's close to the right tube diameter that would work. Any difference in die vs tubing diameter may result in ovalizing a bit. If close you could put stretchable tape on the tube in the area of the bend, that will protect from scratching too.
But better yet, find your local marine
railmaker, and ask about them bending what you need, create a relationship so can get them to electropolish after you weld .