Check for traces of mice and rats every so often. They can make a rig completely uninhabitable if not caught and dealt with.
Run the furnace every so often to ensure that it works.
As above, the main things to address are winterizing, keeping the chassis and house batteries shipshape, running the generator (Onan has a method to fog it for storage, but it will work to run the generator every couple of weeks for 30-45 minutes under a half load (an electric heater should do the job.) Just don't let the gas sit stale too long.
I've always wanted to place a fuel petcock on the generator's line. That way, I can turn the valve off, then let the carb run dry, which means no gas in the bowl to turn into varnish, and require a new carb rebuild.