Using one of the 12v ultrasonic ‘cool mist’ humidifiers/foggers (order spare discs with it btw - they can be hard to find later) - put it in a bucket/resevoir with a 100w aquarium heater set to your minimum temp. Make sure the fogger is set on a humidistat - also it doesn’t get immersed - should float just a little under the surface.
That way you bring in heat, thermal mass to help maintain the heat + controlled humidity.