A vapor-liquid separating space is provided in a body. The front cross member and the sub-cross member are coupled by a backbone brace which is secured to the front cross member and the sub-cross member at positions in right and left portions of the front cross member and the sub-cross member by bolts or the like. One aspect of the invention relates to a latch that is placed in a recess when the lid is opened so as to eliminate unsightly and harmful protrusions. Next, the metal is chemical-mechanically polished to form a metal line. The collecting channel is covered by floor plates, which can be walked upon or swung up into a vertical position, and which are provided with exhaust slots extending in the longitudinal and transverse directions, it being advantageous for the total area of the slots be a function of the discharge of exhaust air and the velocity of the exhaust air.