I follow the recommendation of the US Army Corps of Engineers Cold Regions Research & Engineering Laboratory
Cold Regions Technical Digest
No. 91-4, May 1991
Automotive Batteries at Low Temperatures
a239115.pdf
"Batteries should be stored in a cold place, say, about -15°C (+5F), although when fully charged to a specific gravity of 1.280 or greater they can be stored at -1C indefinitely without deteriorating.
In addition, all batteries experience some degree of self-discharge during storage. This can be greatly reduced by storing them at lower temperatures. If a piece of equipment is to be left for a long period, it is best to remove the negative terminal, as the parasitic electrical loads in most equipment will eventually drain the battery. Most vehicles normally have a small, continuous discharge on the battery of as much as 20 milliamps due to digital clocks and other electronic devices. In addition, there may be a fault in the vehicle's electrical system that can discharge the battery even when all the accessories are turned off. This is especially likely in extremely cold areas, where wire insulation may become brittle in the cold and crack or break away.
Batteries should be kept clean and dry, as they will slowly discharge through the film composed of dirt and small amounts of acid that tends to accumulate on the surface. The battery can be cleaned using a solution of baking soda followed by rinsing with clean water. This will also prevent corrosion of the posts. Anti-corrosion rings also reduce this problem. These felt rings, impregnated with a compound that neutralizes the acid, fit over the positive terminal beneath the connector"
Based on info in the document a battery at 50% SOC doesn't freeze until about -35 F.
I leave my battery in the battery box on the a-frame. Only reasons I see to pull it is if there are worries about it getting stolen and when it needs to be replaced.