Don't put things directly on the ground. The sun pulls moisture up all the time.I would consider building a platform of pallets, covering that with plastic, placing the parts on it and folding the sides of the plastic up leaving an opening at the top and under the shed roof. That should keep things dry and allow it to breath.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles