I just thought of this now. You could get a piece of sheet metal or plastic that is long enough to start at the front of your cab to the back cross bar on ladder rack. Rivet to the back cross bar, front cross bar and let it droop down to you cab in front. Having that end held down by an end cap that is stuck to cab with 3M double sided tape. Don't think you would want to mess up your roof with rivets.
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