I take mine out of the RV and place them in a garage that stays above freezing; around 40 or 50 degrees. I then check the electrolyte for specific gravity and trickle charge to at least 1.27 and then disconnect from the charger and place a digital voltage gauge on it. (draws no power until the button for display is pressed) I check it for 12.6 volts and specific gravity maybe once or twice during the down time. I've never seen the voltage change from 12.6 or the specific gravity drop below 1.265.
I suppose it's overkill as just charging them and leaving for 3 months wouldn't have changed anything.