Yes, fully charged battery will not freeze.. You will have to monitor the pack to see how long it will take for the charge to drain off of them. I would check it 30 minutes after a full charge and then one week after. Find out where it drops to about 49v (others may suggest higher?) and recharge. and monitor again . I'm thinking every one to two weeks depending on the condition of your batteries and connections and the severity of the weather.Don't forget to check the water levels....outside with a tarp IS worse case senario....hope this helps
I think inside would be better but you will still have to charge and moitor them.