I have found that the space under the bed is just the right size for most of the box sizes. And it keeps the dust bunnies from making a home there. You can also line the back of your closet with them, about two layers high dosen't affect your cloths. My son has a collections of stamps that he is covering the wall with on poster board, maybe you could build a wall in the den or play room? They are bound to have some insulation quality to them.