First, storage on concrete is no longer the evil it was decades ago. Battery cases are made of better materials, and the self-discharge is no greater sitting on concrete than sitting on wood.
The biggest killers of batteries is leaving them hooked up without any recharging for an extended period. Almost all vehicles with batteries, including cars, RVs, and as I learned the hard way, even lawn tractors, have parasitic draws which will discharge a battery in a matter of weeks (or sooner).
In freezing temperatures, a discharged battery can freeze up, and the ice can split the case. A fully charged battery will do just fine down to about -20 degrees F or worse.
What works for me in Colorado winters is fully charging the battery, and then disconnecting it (leave it in place or store in the unheated garage). Since we have up to 7 months of freezes on cold nights, I do recharge the batteries once or twice during the winter. And then reconnect and recharge for 1st use in Spring.
Trickle chargers (solar or electric) are another way to keep a battery fully charged while in storage. With trickle charging, you should probably check the battery water level periodically to make sure the battery is not being overcharged and losing water. Overcharging is actually more likely if the parasitic loads are left attached, which may/may not send the charger into a higher voltage mode.
I finally got smart on my A-frame and installed a battery cutoff switch to eliminate all loads when I'm not plugged into house power or a tow vehicle. Saves unhooking and re-hooking wires all the time.
2014 Rockwood A122 A-frame
dual 6V golf cart batteries