Small piece of square stock with a weld-in pull pin.
Smaller piece of square stock that will fit inside the first piece of square stock. Length to be determined by how high you need it. Drill 2 holes in this piece to accept the pull pin. One hole for down position, one hole for up position
Weld the first piece to your existing rack. Use the appropriate hardware to attach the awning to the second piece, and attach awning.
Slip the second piece in the first piece.