I'm seeing a lot of posts on the topic from folks in Texas right now (we're Texans but not in Texas at the moment). If you run the main furnace rather than space heaters, it should keep the basement from freezing. We're in a fifth wheel rather than a motorhome, but we've weathered temps as low as 10 - 11F with high winds and survived.
Rob
U.S. Army retired
2020 Solitude 310GK-R
MORryde IS, disc brakes, solar, DP windows
(Previously in a Reflection 337RLS)
2012 F350 CC DRW Lariat 6.7
Full-time since 8/2015