A firefighting training unit and a method of fabrication such a unit. The fabrication involves modifying an existing structure such as a steel cargo container. The modification procedures first require that combustibles be removed and a steel floor welded in place of the existing wood floor. Viewing ports and access doors are provided in the sidewalls. Roof ventilation vents are cut in the roof and the opening controlled by a hinged hatch. The units are economical, mobile and may be used for both fire training and forensic investigation.