Unless it remains cold for a long time, the high heat capacity of the water in the tub will keep it from freezing. As far as the pump compartment, a 100W light bulb can do wonders. All other pipes, etc., may be a cause for worry if the temp drops too much although a tarp over the tub along with the residual heat from the light bulb and tub should keep it cozy for a while. You can also add more bulbs under the tarp if you are concerned.