Abstract: A mounting structure for vent systems on vehicles with metallic roof tops including a rigid frame adapted to be welded to the perimeter of an opening in the roof and projecting vertically above the surface of the roof to form a barrier to the passage of moisture. The frame is covered with a resilient frame, one portion of which acts as a seal between the rigid frame and the vent and the remainder of the resilient frame acts as a molding concealing the weld between the rigid frame and the roof of the vehicle. The rigid frame is provided with captive fastener elements which receive complementary fasteners for retaining a vent on the roof structure of the vehicle and at the same time permits easy removal of the vent in the absence of access to the interior of the vehicle.