We have a vacation grade Winnebago class A that we spent a few years of living in, part time. We have spent a limited amount of time in cold weather, with daytime temps in the thirties, and nights in the teens. Bottom line is that it's doable and nothing but a total pain in the ass. These things are typically pretty poorly insulated, and when it gets that cold, they suck propane like mad. I was getting about two days out of a portable 30 lb cylinder. They also develop severe issues with condensation and typically the windows are soaked, with water dripping down the walls, if you don't pay attention. "Surviving" in an RV in severe cold is something that a lot of folks do successfully, but IMHO, it's uncomfortable and expensive. There is a lot of info. online, including videos of folks who really go to extremes.
As for the winterizing question, it's always best to use antifreeze. Now there are internet experts out there that swear you will never have issues with just using air, but here is the thing. If you ask an RV dealer about it, they will tell you that they use antifreeze on their own inventory. This can be pretty evident when you tour RV lots in spring, as there are pink stains in the sinks and toilets. If air worked so good, deals wouldn't be paying their help to pump hundreds of gallons pink stuff in their inventory. I'm concerned that you are thinking of paying to have this done. As a serious RVer, IMHO, the only way RV ownership doesn't turn into a money burning fountain of waste is that I DIY everything I possibly can. Everything from maintaining and replacing batteries, 12volt converter, thermostat, and other parts of the house systems, to doing oil changes and vehicle maintenance. Even if I can't do it myself, I carefully control the work being done, and look for the most economical way to do it. I just had to do a lot of axle and brake work on the rear end. Since I would of needed a flat concrete work area, a 10 ton floor jack, and other very heavy tools, I had to sub it out. I took it to a well regarded independent repair shop, NOT a big rv dealer. This place gets just over half of what Camping world charges, per hour, and won't screw me, like CW has. Once they had the thing apart, I spent a few minutes going over the job with the shop manager and mechanic. In the end, I added a flush and fill of the rear axle oil, and had them replace the sway bar bushing with OEM parts, and still came in under the original estimate. The whole thing was a painful deal, at $1250, but it could of easily been twice that at a big RV "mega-dealer". I needed new tires and the honest shop that did the work quoted roughly $2200. By buying online, and having a heavy truck shop take delivery of the tires and install them, I spent $1600 on the same tires.
When it comes to RV DIY, winterizing is about one of the easiest tasks. First you need to determine if you have a winterizing set-up installed at your water pump. this is a few valves that need to be flipped, so that a short hose can be used to suck antifreeze out of a gallon bottle. If you need to have this installed, it's well worth the small expense. Then it's just a matter of removing as much water from the system as possible, by draining any low point drains, the fresh water tank and water heater tank, then running the pump and flush the remaining water into the sinks and toilet. Then it only takes a few minutes to suck some pink antifreeze into the pipes and get it to flow out of the faucets, shower and toilet. The final step is dumping some pink in the drains and toilet. Once you learn how, it's literally a ten minute job with $5 worth of antifreeze. At a dealer it can easily be a $100+ fee to do the same thing.
