No, you should not install your APEC ROES-50 in an unheated garage.
The system must be installed indoors in a sheltered, temperature-controlled environment. An unheated garage that gets cold in winter exposes the system to freezing temperatures.
Water inside the filters, membrane, and tank can freeze. This will crack the component housings and cause irreparable damage to the system.
For proper operation, the feed water temperature must remain between 40°F and 100°F (4°C to 37°C). The installation location must also be protected from direct sunlight and weather extremes.
Choose a protected indoor location like under the kitchen sink, in a basement utility room, or in a conditioned crawl space. Installations in environments like an unheated garage void the warranty.