A corner piece is configured for rigidly joining together a pair of beams to form a frame. A main body includes a pair of pegs diverging outwardly therefrom for being inserted in corresponding sockets in respective ends of the beams. The body includes a crotch laterally separating the pegs at an inside corner for engaging the beams. The crotch permits inside welding to the corner piece. And, in a preferred embodiment, a corner bezel extends from the body to define an outside corner, and a corner seat is disposed in the body for receiving a gasket.