When I owned trailers I took the batteries out and stored at home. Checked voltage each month and charged if needed.
With the motor-home (since 2006) stored in a lot without shore-power, I added two 9-watt solar panels. One for the chassis battery, and the other for the pair of T-105's house-battery bank. The panels do not require a controller and are connected 24/7. In the winter they are moved down from the overhead bed window to the dash panel since over-head bed keeps snow off the windshield.
I check the MH once every month to check batteries with a multi-meter to note state of charge, and run the generator, and engine to exercise them. The original batteries lasted 9 years (chassis) and 10 years (house) on the 2003 MH.
Note that the batteries only get charged otherwise when plugged into shore-power if camping on an electric site, or using the generator. This type of usage obviously did not cause early demise of batteries.
I do monitor charging with a clamp-ammeter for amp-rate, and voltage (at the battery-terminals) to insure all charging methods are working; converter/charger, alternator, and solar-panels.
If batteries are sufficiently charged they will not freeze in cold weather. Also; cold weather storage is much better than hot weather storage as mentioned in an early reply.
Mark & Jan "Old age & treachery win over youth & enthusiasm"
2003 Fleetwood Jamboree 29