A corner rail extrusion (124) is disclosed for facilitating the sealing of joints at the corners of structures such as recreational vehicles. The corner rail extrusion (124) includes a pair of outwardly and generally perpendicularly extending legs comprising a first leg (126) and a second leg (128). The rail extrusion (124) also includes a central bulbous interior (130). The central bulbous interior (130) is positioned so as to span a corner formed by a side wall (104) and rear wall (106), with the bulbous interior (130) essentially "fitting into" a gap (122).