There are eleven chests in the Arid Badlands (DLC4) area.
Location 1 (2 Red Chests)
Transition point, before the gate. There are two Red Chests and numerous ammunition crates here.
Location 2 (7 Red Chests, 2 White Chests)
Go through the gate and around the perimeter of the map. Use caution as going near Marcus' bus will trigger the cut scene and the MINAC fight. All chests can still be looted during and after the fight.