You can try opening up a few containers of baking soda. That will absorb SOME moisture and odor out of the air but without a dehumidifier you are rolling the dice with powdery mildew. I only run my dehumidifier at night during flower because it uses so much electricity and raises the temperature and I am pulling 70 pints a night out of a small room with 6 plants. Sorry to say but I am not wasting 3 months of work to powdery mildew. I beat the fungus gnats, then the mites, now the humidity of a Oregon winter. Growing indoors has been extremely challenging this time around but somehow I was able to overcome. I am sure you will to. Get a small bathroom dehumidifier. That is all you need for that small room.