This applies to all PCs with tank heaters. They heat just the gray and black water tanks, nothing else. The 12v heating pads are bonded to the underside of the two tanks. Then the tanks get wrapped in a foil-looking insulation. You won't be able to see the heating pads.
The rest of the motor home plumbing & fresh water tank is inside the insulated rig. As long as the interior is kept warm, nothing should freeze. But there are limits. I would imagine that you'll have trouble under subzero conditions.
I think the most vulnerable things freezing are the dump valves, based on stories read on RV forums. The tank heaters will radiate warmth only so far down the pipes.
