Branches would hit them if they were higher than the rack, so they would have to be low, or protected good. And I saw pictures of them bolted onto the roof rack with u-bolts; I didn’t think it looked as clean. And maybe there is less stuff to rattle.

EDIT: I ground the paint off with an angle grinder before I welded it. I guarantee that weld will NEVER break.

On my old isuzu trooper I had the same lights welded onto the same spot, never had any problems.
http://204.210.136.14/trooper/08/PA290021.JPG