Key word is dew point. You don't need to heat it for comfort, only enough to keep condensation under control. Use paste wax on bare metal for added protection. LP can put moisture in if too much is used without vent. Insulation is the cheapest as it is a one time expense and will lessen fuel need thereafter.
Keep in mine that cycling heat up and down cast will be cold and will condense, so infrared over that equipment or circulating fans will help as would dedicated insulated covers with small electric rod type heaters.