For the most part, you can really store your model where you see fit. Clearly, it may not be advisable to do so in direct contact to the sun as the UV rays can cause damage. But, once it is either folded or rolled up, you can stow it away in a closet, under your bed, or any other location you can think of where it will not be damaged. Now, you should also avoid folding your model in an unintended manner as this can cause creases.