I have found that it has to get down below 20 degrees at night for my freshwater line at my pump to freeze. 100 watt bulb and foam wrapping in the compartment works.
A lot of Class A heaters are ducted to the basement compartments to keep them from freezing. Maybe yours does too.
As long as it gets above freezing during the day I don't do any problems.
I have heard of people putting a small amount of RV anti freeze in the gray and black tanks. But I have never had any problems dumping in the winter.
06 Hurricane 34FT WH W20 Chassis 8.1L 120K, Steersafe, Koni Shocks, DIY Trac Bar, Tri-Metric 2025RV Battery Monitor, 4-6V Batteries, Scan Gauge 2, Crossfires, 735W Solar Morningstar MPPT-60, KVH R5 In-Motion Sat, XM Radio, 07 Chevy Malibu Maxx Toad, Falcon 2, Brake Buddy, Escapee