Yes, you can. JD Mini Storage always recommends using the same-sized boxes for your items. Using boxes of the same size makes it much easier to move and stack things. It also reduces damage from larger boxes caving in smaller ones beneath them. That being said, smaller boxes are better for books. Smaller boxes save space and allow you to store more of them in your storage unit. Your boxes will accumulate a layer of dust while stored, and our units are not climate-controlled. Please take dust and the environment into consideration when packing and planning the amount of time you will need your storage unit.