I'm starting to wonder how difficult it would be to add a window or two on the exterior wall and an exhaust vent/fan in the ceiling to the attic.

Long term would be insulation in the exterior wall, with short term adding insulating to the garage door and finding a way to help it seal around the sides.

Short term, a second fan to pull the air in on the wall and another to push it out creating a good airflow pattern would also be helpful. I need to do more research on evaporative units and the ductless units by Mitsubishi as well.