Well, I've been in the HVAC business for 10 yrs and can tell you what I would do. Assuming you have an outside wall, I would install a "window shaker" air conditioner that vents to the outside. 8,000 to 10,000 BTU is what I would prolly put in there. I would also get a dehumidifier that I could run if I didn't need too much cooling, although just running the dehumidifier will also keep the temperatures down somewhat... because its basically a partial air conditioner if you like.

keylime