Abstract: A plurality of members for temporary assembly into a rigid branch structure for supporting a cover to form an enclosure, including a plurality of elongated rigid, hollow posts defined by opposed pairs of flat post walls joined together along their respective marginal edges between spaced-apart terminal ends, the walls having formed therein at least one pair of apertures in spaced-apart, opposed relationship near each post terminal end and a series of elongated ribs extending inward from the walls and along the lengths of the posts between the apertures, a coupling for axially joining one post to another in rigid, axial, end-to-end alignment including a butt plate for transverse positioning between the terminal ends of the joined posts, at least two stems extending outward from the butt plate for insertion a distance into each hollow post end, each stem including two pairs of closely-spaced webs arranged in spaced-apart configuration and defined by opposed marginal edges spanning between the opposed walls of t