hurricane 2007 34n motorhome

My guess is your "heated" tanks are actually passively heated with some residual heat from the furnace ductwork and not actually actively heated. If it gets above freezing during the day I would imagine that a full FW tank would not freeze. I also suspect it may not be your tank as much as your lines and pump. The issue with heat tape is you never know when it stops working. Usually light bulbs in wet bays are enough to prevent freezing but 13 degrees is pretty cold. Opening your cabinets and allowing heat to hit the plumbing also helps. But camping in 13 degree temps without a rig designed for it is prolonging the inevitable. When we would camp in temps that cold we would winterize and use the CG restrooms. I've had my water pump freeze more than a few times, even with a light bulb.