I used to pull the batteries, but since they started to get heavier, I stopped the practice.
To leave them in the trailer when it's freezing out, you have to keep them fully charged. But then I don't live in AK. A 100 percent fully charged battery will not freeze until approximately minus 76 degrees F. So says Google.
As my trailer is covered and parked at home, I top off the water, and throw the disconnect after they are 100% charged. Periodically hook up power to the trailer and let the converter/charger do it's thing.
If I were leaving the trailer in a storage yard, I'd be inclined to pull them and the LPG. As much for theft prevention as charging convenience.
If I lived in colder then AK temps, and it was getting to -76F I'd move, but you can pull them. Better yet, have someone else pull them. If the garage has power, leave it hooked up so the converter can take care of it. Do check/fill the batteries a couple times a year.