I replied to this yesterday but clearly I had an issue...don't see it now.
Anyway, others have said pretty much what I did.
You'll likely get into colder stuff than I've been in, but we have used the RV in weather right at freezing a bit.
I'd plan on running the furnace a bit but not rely on it for your only heat. It will drain your tank in nothing flat since it will run nearly all the time. (and I personally wouldn't want to sleep with it on). Instead I'd want to make sure the power source is good and use a couple of electric space heaters.
I'd try to park out of the wind as much as possible to minimize both the drafts and chill inside, but also to help in keeping my tank drains from having problems. On that note if it turned out to be a seriously cold weather system on those days I'd probably plan on using my tank heat pads and probably poor some antifreeze in the tan bottoms just to protect those valves a bit. I've been ok though without doing this.
Also, I'd use my reflectix window shades and my roof vent 'pillows' for added insulation.
One other thought... since you're with family this request would be a little easier I think.... I'd plan on running more than one electric heater, and at least one of them I'd run on an extension cord connected to a different circuit.... guessing you'd be plugging your 30A through a dogbone into their porch or garage outlet. Having a heater on a different circuit would hopefully give a little insurance against tripped breakers or GFCI's when you might be asleep or away.
my main concern would be keeping the house warm enough to protect your fresh water system. I could be wrong but I recon if it comes down to it if the waste tanks freeze it'll only prevent you form dumping. Not likely to cause serious problems....again just a guess though.
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