You may have to go with a group 31, it is a little larger capacity than the group 27, and normally will last a bit longer. Not nearly as long as good golf cart batteries.
IF you keep the battery charged, then they typically will not freeze. If you can not plug them in at home, then I suggest removing them and storing them in the garage (keep them off the concrete, it conducts away to much heat) and keep them on a battery maintainer, that can put out about 1 amp per hour.
Trojan, Napa and others make group 31 batteries - just make sure it is a deep cycle, more than one designed to start engines. It also MUST have a place to add water if you want it to last more than 2 years.
Fred.