STORING TM IN AN OPEN, UPRIGHT POSITION?

We have a goodsized barn with a large, open driveway area where our TM 3023 will be stored during the winter months. We are considering storing it fully opened since there is plenty of space to allow for this, and it then becomes quick and easy to access for whatever reasons we want to get into it like checking on its general condition and readying it for a trip. (We are making careful anti-mouse preparations.) Are there reasons (aside from the whole thing getting a bit dusty) why we should not store the TM open in the barn?