I agree, storing them outdoor may not be safe. You can create a separate chamber of their actual size so that they can fit in easily and don't consume the extra space.

I wouldnt recommend storing these outside in the weather.....someplace inside only.... tires i would store on a pallet with tires of same size stacked two high and on the floor...forks can be stored along a wall so are out of the way...of course this all depends on how much you stock and the area available...but one thing not to do is store them so is hard to get to them as they are a heavy and item.....