Battery winter storage

Unless you live in someplace like Alaska where the low temperatures are very far below zero, there's no need to bring the batteries in from the outside (unless logistics of e.g. connecting a maintainer dictate, of course). A fully charged battery will not freeze. If anything, the cold is better for preservation, as the self-discharge is lower at lower temperatures.

Think about how many vehicles are parked outside throughout the winter, and their batteries are okay even after sitting for many hours in the cold. RV batteries are no different. The cold is not damaging in and of itself.