Best way for winter battery storage

[Sopper]

I am in the final stages of my first winterization of my Trailmanor 2720 and had some questions about the batteries. As you can see in the attachment, my TM has two batteries. My TM is also going to be stored when not in use, and during the winter, covered in one stall of my three stall garage. What would be the best way to store my batteries, long term, to encourage them to survive over the winter?

1) Unplug the batteries from the camper and let set in the garage.

2) Unplug the batteries from the camper, remove them from the camper frame and store them in my basement.

3) Unplug the batteries from the camper and install a trickle charger to both batteries (in series) powered in the garage

4) Unplug the batteries from the camper, remove them from the camper frame, store them in my basement and connect them, in series, to a trickle charger.

I want to do what is best for the batteries, and the camper, over the long Minnesota winter months. Your comments, suggestions and experiences are welcome and appreciated!