If it was me, I would periodically (maybe weekly?) remotely activate the HVAC system for a few hours. Before I left, I would make sure the HVAC system was using external air source because you cannot change re-circ setting remotely.
Is the garage connected to the house? Is it climate controlled? I'd leave the windows open a bit.
If it is in a garage that has a high humidity, I would leave a dehumidifier in the garage at a reasonable setting and connect a hose that runs outside under the garage door so the dehumidifier can run while you're gone.