39 and ends are knotted at the outward face of wall portion 39 to prevent movement thereof through apertures 124 and 126 apertures 124 and 126 are positioned directly above and directly below respectively aperture 116 cord member 120 is maintained through apertures 128 and 130 in position securing member 49 adjacent wall portion 39 and through slots 132 and 134 in position securing member 49 adjacent wall portion 37 when tongues 110 and 112 are positioned through apertures 114 and 116 loop section 136 of cord member 120 is stretched and positioned over ear 138 extending from wall section 140 of wall portion 37 the overall length of cord member 120 is such that when loop section 136 thereof is stretch over ear 138 cord member 120 is taut thus urging tongues 110 and 112 into apertures 114 and 116 and thereby wall portions 37 and 39 into firm engagement with position securing member 49 turning now to fig8 through 11 movement of wall sections 37 and 39 and position securing member 49 from their operable engaged positions as shown in fig1 to their stored positions is illustrated wall portions 37 and 39 each include pivotable angled attachment sections 142 and 144 and 146 and 148 respectively angled attachment sections 142 and 144 are formed by sections 150 and 152 and 90 u00b0 angle 153 and angled attachment sections 146 and 148 are formed by sections 154 and 156 and 90 u00b0 angle 158 sections 154 and 156 are of greater length between the point of attachment at bolts 45 and 90 u00b0 angle 158 than is the length of sections 150 and 152 between the point of attachment at bolt 45 and 90 u00b0 angle 153 with the difference.