Condensation is a system problem
Winter condensation aboard a narrowboat is rarely just one cold window. Moisture comes from people, cooking, drying clothes, wet gear and poor airflow.
Practical checks
Look at ventilation, heating routine, mattress airflow, lockers, window frames, wet entry points, bilge awareness and whether stored kit is trapping damp.
Safety note
Ventilation should not be blocked to save heat, especially where combustion appliances are present. Carbon monoxide safety remains separate and serious.