When a flooded battery sits, the more dense, stronger acid sinks to the bottom and chews more at the plates.
Putting a battery on a colder concrete floor can increase this electrolyte stratification. Wood under the battery in this case would be a temperature insulator.
Some RV converters, when floating a battery, will bump the voltage upto 14.4v for 15 minutes every 18 hours. This will cause bubbling and will mix up the electrolyte to prevent stratification.
Unfortunately this converter maker( progressive dynamics) calls this destratification 14.4v bump 'Equalization', which regarding charging of batteries, is an entirely different procedure.
Cold temperatures are good for a resting fully charged battery as it slows self discharge.
How much self discharge there is depends on the battery itself and its condition at the time of storage.
http://www.pbase.com/mainecruising/self_discharge
Personally, In such a climate in winter, I would ensure the batteries to be stored are absolutely 100% charged via a prolonged absorption cycle followed by a true equalization, and then let them sit unhooked to anything, on wood or some other temperature insulating surface.
Just being able to ensure a 100% recharge will extend the longevity of any lead acid battery. The extended absorption charge and the equalization usually require special equipment to achieve. The green light on any given automatic smart charger, is mocking any human who believes the battery is indeed fully charged.
Check the specific gravity if you do not believe it. Automatic chargers call 92 to 95% charged, good enough and blast that Human soothing green light. The battery thinks otherwise.