Mini-catalytic heater for keeping tanks warm off-grid??

Conventional roof and gutter heating cable is 5w/ft. I have a 60 length of it that I plan to install under my waste tank and against the drain piping. It won't have to run continuously in all but the most bitter cold. With an insulation board or pipe wrap and a sheet of aluminum between the heating tape and the outdoors, I'm thinking a duty cycle of 1/6 will keep the tanks and pipes from freezing.
My freshwater tank and supply piping is inside the cabin so no worries there.