As long as its dry it should b fine stored in a garage IMO… i have an acrylic tank stored in my ohio garage atm… there is expansion/contraction of both acrylic and that poly tub but the builder used a rubber gasket so id say its safe there. If the seal was silicone id b worried of it tearing loose. Very smart way to build with the rubber gasket. Buddy of mine moved an acrylic tank this time of year with terrible results. The tank had a shotty piece of 1/8” acrylic poorly glued in as a background. The water was behind the sheet, froze and cracked it everywhere along the seams. Not a typical scenario.