a secondary containment capsule for enclosing primary storage tanks made of one or more standard axial portions and end caps is disclosed . each of these segments are separately molded from a curable plastic material such as fiberglass reinforced polyester . axial segments are separately slid over the primary tank and joined together at their mating ends , forming a longitudinal cylinder covering the longitudinal sides of the primary tank . the molded end caps are then placed over the outer ends of the longitudinal cylinder formed by the axial segments to completely enclose the primary tank . the same end caps and axial segments can be used for enclosing primary tanks having the same diameter but different lengths . in another embodiment , the one or more substantially cylindrical sections of the secondary containment capsule are formed on a male mold and split longitudinally for removal from the mold . such section or sections are then clamped around the primary storage tank and rejoined on the split , with molded end caps also being bonded in place . this facilitates removal of the section from a suitably textured mold , easy placement of the split section over the tank and the light clamping of the section around the tank until rejoined , providing the desired fluid migration space between the tank and the containment capsule without looseness therebetween .