Batteries that are discharged can crack in freezing weather. The fluid in the battery freezes and can crack the case like when you forget to turn the fridge down and your diet coke freezes and bang you got a mess.
Look the batteries over for signs of fluid loss or cracking. Check the water/acid level to make sure its correct and use distilled water for top up's if needed. Its so much nicer to have the sealed kind of battery....
I would first plug trailer in to 110 and wait a few hours then unplug to see if you have any juice in the batterys. If so I think your good to plug back in and let the trailer do its work. If not, give them a charge with a battery charger after unhooking from the trailer so they are stand alone. Most people dont do this but I'm always worried about the expensive circuit boards in the fridge ect getting fried.
Please use glasses and gloves when messing with batterys....
Hope this helps you,