Use a king mattress cover for a king mattress or thick queen mattress/boxspring.
King Mattress Cover
$11.95
Description
Mattress covers are essential for moving or storing your mattress, box spring and sofa cushions. Easily and safely protect your mattress against dust, dirt and water while moving or storing. They slip on and off easily and only need some tape to seal the opening.
Remember to order additional bags for matching boxsprings.