I dunno... running a heat tape into someone else's unit could open you up to liability if it froze up or caught fire. Force the owner's hands, even if the owner is a bank.
Many condo associations where intermittent occupancy have a minimum temperature rule built into the bylaws for exactly these kinds of reasons. (eg. My MIL has place in Maine with a 50F min-temp rule that's primarily her summer place. In January only about half the units are occupied, but in July it's full-up.)