You have a couple of options:
1. Fully charge the battery and then disconnect it.
2. Leave the coach plugged in to shore power all winter (this is what I prefer).
3. Keep the battery on a trickle charger.
4. Remove the battery and store it inside.
5. Run the genset an hour every couple weeks (this is my second favorite method).
Most coaches have some latent electrical system loads which will slowly deplete the coach battery. If you do not do something, the coach battery will eventually drain and be susceptible to damage.
I like to keep the coach plugged in to shore power which will help keep the battery from discharging. If I am unable to do that, I run the genset an hour or so every couple weeks to top off the battery and also exercise the genset.