Abstract: A body wall having a horizontal length and a vertical height and including a plurality of elongated upstanding panel members spaced along the wall and including adjacent laterally overlapped longitudinal side marginal strips. One marginal strip of each pair of overlapped side marginal strips is generally planar and the other marginal strip is slightly laterally offset to one side of the corresponding panel member and includes laterally spaced generally coplanar opposite longitudinal marginal border portions and a longitudinally extending central channel portion disposed between and formed integrally with the border portions with the central channel portion opening toward the aforementioned one marginal strip. Securing structure secures at least longitudinally spaced portions of each of the border portions of the other marginal strip to corresponding portions of the one marginal strip toward which the central channel portion of the other marginal strip opens.