Moab is a fun place, but it does have an actual winter, complete with snow and sub-freezing temperatures. Beautiful, but it requires winter camping preparations. Zion NP has a winter but it is much shorter and milder. The Utah snowbirds flock around St. George, which is lower in elevation than Zion, and has a winter comparable to South Carolina, but it has turned into a city of some proportions, so it might not suit those wanting the great outdoors. St. George is within striking distance of Zion, and Zion is close enough to Bryce for a day trip or overnight for anyone ready to return to a mountain-elevation winter. Bryce is technically on the edge of a plateau, but the elevation is high.
It looks like the Bryce Canyon lodge within the park is open all winter Winter at Bryce Canyon - The Lodge at Bryce Canyon
and this would be a fun way to see the park while the AS is parked at a warmer location. I believe the lodgings at Ruby's Inn Lodging in Bryce Canyon
just outside Bryce Canyon NP are open in winter, as well, although their RV park will be closed in winter. There are some other accommodations just outside the park, but someone else would have to do the research on them.