A nested shell enclosure covering behind the cab gaseous fuel tanks on a three dimensional structure. The method and system provides a releasable enclosure around the structure or a rack or the like formed by attaching a plurality of shell components which nest in a sequential pattern over the structure via housing latch assemblies formed on the interior wall surface of shell components to catch bracket assemblies attached to the structure and wherein the latch and catch assemblies releasably affix the enclosure shells to the structure and together without the use of threaded fasteners; and, wherein the shells components are nested and evenly disperse force along the perimeter edges where the shells overlap.