I have said this many times in the past, but here is another repeat. All you need to do is this for winter storage is:
1. Be sure the batteries are fully charged.
2. Clean the tops of the batteries.
3. Disconnect the wires from the negative terminal(s) so that there is absolutely no way the batteries can be connected to anything and be discharged.
There is no need to remove them. There is no need to trickle charge them. They will not freeze if it is above -40 F. Battery self discharge is increased by them being nice and warm. When cold, the rate of self discharge is decreased.
In the spring, re connect the negative terminal, and use the built in converter/charger in the Airstream to bring what little discharge that has occurred back in.
I have had Airstreams since the late 1970's and this technique has worked very well for all of those years. I have never had any battery damage. My battery life is in the range of 8 to 10 years.
And others will disagree with me. But charge, clean, then fully disconnect will work just fine in any cold climate. No need to break your back removing batteries.