A support member includes a plate and an engaging member formed to the plate. The extends laterally and is defined by an upper surface, a lower surface and a rail that extends downward from the lower surface proximate an outer edge of the plate. The engaging member is formed to the lower surface of the plate and around a portion of the rail. The engaging member includes a surface engaging shoulder extending downward from a lower surface of the engaging member and formed around an outer surface of the engaging member. The surface engaging shoulder extends outside of and below the rail. The engaging member includes an upper shoulder formed above the surface engaging shoulder. The engaging member is configured so that the surface engaging shoulder and the upper shoulder flex upward when a force is applied downward to the upper surface of the plate.