Anything you do to warm it will be somewhat undone by the massive airflow of running the forge sucking in ambient air. If your shop is below operating temperature, warming the forge alone won’t be enough.
I have a small space and use a 1500 watt delonghi oil filled radiator style space heater. I leave the forge door open to let heat into the unit, and leave the space heater set to 60 degrees overnight.
Heater recommendation came from the wirecutter: