I suggest plumbing antifreeze for all the drains. Treat the water pump with antifreeze too.
Does the fridge have an ice maker?
Give yourself a pat on the back for being a great friend to the widow.
Regards, Don
My ride is a 28 foot Class C, 256 watts solar, 556 amp-hours of Telcom jars, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.