I live about 4 miles south of IH 10 near San Antonio. I've done some manner of winterizing every year. Sometimes I just drain the lines if chances of freezing are pretty low before my next anticipated use. My normal process is to just blow the lines with air. It's easy and quick, and I'll dump AF in the tanks and sinks at that time. But I can remember a couple cold snaps where I've put AF in the lines just to be safe. Below freezing multiple nights with nasty weather during the day not warming up much, I could see the lines freezing, and it's not worth the chance to me.
All that being said, I was using my camper in Junction last year for a deer hunt. The temp dropped into the low 20s at night, and I froze the line between my fresh tank and my pump. Didn't break anything, but it did indeed freeze enough for no water to flow to the toilet when I got up for "nature's call".
I used to live in Austin, and there were a few times where I would have winterized a trailer if I'd had one.
Being stored on your property or in your driveway kind of changes things a bit though. You can leave heaters on, and you can put hot lights under the camper in strategic places for the one or two times where an extended hard freeze is a real possibility.
-2018 Greyhawk 29MV
-1997 Jeep Wrangler YJ (Toad)
-2015 Jeep Grand Cherokee Limited (Soon to be Toad)
-2014 Jay Flight 28BHBE & Ram 2500 6.4L CC 4x4 (sold)