upper band 30 in the upper portion 32 of pocket 26 a plurality of springs 34 interconnects bands 28 and 30 turning now to fig2 and 3 partial views of the truss or spring assembly 24 are shown the extended view fig2 with the sidewall 16 erected most clearly shows the construction the s shaped springs 34 and bands 28 and 30 which are fabricated from tempered spring steel are crimped and clamped together as described in more detail below the band 28 is exemplary of the clamping affixing arrangement used also for band 30 and at either end of each spring 34 the spring material is substantially rectangular in cross section having two edges and two faces and the material bends or folds in a plane substantially normal to the face for attaching each spring 34 two crimps 36 and 38 are made in the receiving portions 40 and 42 of bands 28 and 30 respectively in each spring 34 two corresponding nesting crimps 44 and 46 respectively are constructed compression fittings 48 and 50 are provided holding the two receiving portions 40 and 42 to the corresponding crimped sections 36 38 44 and 46 nesting one within the other the compression fittings are preferably of a tubular malleable metallic body which is conformed by pressure to the juncture optionally the joint is completed by covering with a heat shrink tubing 52 which after emplacement is heat shrunk to cover the corners and edges this prevents tearing of the urethane nylon laminate during erection of the tank the springs 34 are connected in a similar fashion to bands 28 and 30 except that prior to affixation each spring end portion 54.