i doubt you will get the odor out of cardboard. I use white vinegar (neutralizes urine odor and makes everything smell like vinegar) then rinse with water, then sprinkle on baking powder to remove vinegar smell. Then a few days later, final rinse with water. this works well on metal surfaces. Pay attention to hantavirus (wet the mouse wastes and wipe up, don't make dust by sweeping or vacuming).
