Most Class A's with enclosed tanks are rated for down to 20 degrees
For lower temps (Teens) you can add heat to the wet bay.. 3 options
1: Small heater
2: Peal and stick heat panels that attach to the tank
and the option I chose is:
3: Lights.. On my rig there is a gap between the bottom of the fresh tank and the bottom of the compartment.. I put a string of C-9 Incandascent Christmas tree lamps in there.. These are the old "Outdoor" type 9 watts per lamp = about 270 watts for the string.
I put a 100watt lamp in the other end (Waste end) of the pass through bay
Since doing that I have had one day where one pipe froze (And thawed with no damage) it was like 11 degrees that night.
I have had outside lines freeze several times.. So my fresh hose is also light up with a string of incandescent rope lights duct taped to it
All lights are controlled by thermostats Plug adapters sold for eves de-icers and pipe heat tapes and stock tank heaters at Lowes, home Depot, Farm & Fleet type stores.