First of all, I am fortunate to have indoor storage available for our Roadtrek. For winter, here is what I do beyond winterizing.
1. Keep the gas tank full. Probably not necessary these days, but old dogs don't relearn their tricks.
2. Use a simple battery cutoff switch on coach and chassis batteries. Here is what I use:
https://www.walmart.com/ip/Battery-Cutoff-Switch-Car-Rv-Boat-Truck-Link-Terminal-Quick-Disconnect-Kill-Key/119498120
You can buy them at Walmart or most places for under ten bucks. Make sure the batteries are fully charged before storage. In northern climes, some prefer to remove the batteries and store them inside a garage.
3. I drive my RT about sixty miles once a month for all the reasons others have mentioned. I fire up the generator and put it under a good load (the RT has a heat pump so I just set the thermostat sky high, crack the back windows and use that for a load.
4. I fill back up with gas before putting it back in storage.
I feel that it is imperative to run the generator for at least an hour and some manuals suggest two hours every month as a minimum.
5. Other than that, I protect it like I would any vehicle.