A tie-down assembly is disclosed which includes a plastic guard rail that defines a central floor and spaced, parallel interior walls which cooperate to define a recess, a pair of beveled exterior surfaces disposed outside of the respective interior walls, and an array of slits in the floor. A clamp formed of a folded piece of sheet metal defines a sleeve section disposed in the recess and a shank section which passes through one of the slits in the floor. A tie-down ring is pivotably mounted in the sleeve section and is movable between a stowed position, in which no part of the clamp or tie-down member extends out of the recess, and a use position. Aligned openings are defined by the floor and the shank section of the clamp, and a single fastener can be positioned to pass through the aligned openings in order to secure the entire tie-down assembly in place.