Seal the backglass in a dry environment and put large desiccant packs inside the cabinet. Run a dehumidifier 24x7, and keep the garage as air tight as possible. Try to control rapid fluctuations in temperature and humidity. That's the killer. As long as the environment is relatively stable and not overly humid, it should fare reasonably well.

I helped a friend get a soda machine down from an attic room many years ago. Luckily there was an actual staircase, but it was steep and narrow. Before you was born, Otaku!