I store my camper outside in Minnesota as well and I have always taken the battery out. I put it in a warm place and charge it a couple times during the winter. With the current weather we could probably still be camping
I'll be indoors this year, protected from the elements, but not heated.
I don't know if I really want to pull both house batteries out though.
My rig is an Alante 31V, and I have been unable to determine if the charging system also maintains, or there will be a risk of overcharging while not in use?
Costco has Battery Tenders for around $30. Hook it up plug it in and forget about the batteries until spring. Maybe check water levels a couple of times.
Here in Northern Ontario our winters are cold. I pull my battery and put it in my detached unheated garage. I top up the cells with distilled water and fully charge it. Over the winter I will put it on the charger once a month to make sure it has maintained it charge. I do the same to my boat batteries and have never had a problem come spring.
Your installed converter/charger is a three-stage battery charger and will take care of things if you leave it plugged in. OTOH, checking the water level, fully charging the batteries, and disconnecting them won't cause any harm either.
Another important note is to either run the generator out of fuel by disconnecting the fuel line while running before storing it, or run it for at least 60 minutes each month with a 50% load such as an air conditioner.
The Onan gas generator carburetors are known for gumming up if left with fuel in the bowl for too long.
I store my camper outside in Minnesota as well and I have always taken the battery out. I put it in a warm place and charge it a couple times during the winter. With the current weather we could probably still be camping