Abstract: A buried vault enclosure of fiber reinforced plastic, wherein earth material, such as dirt, sand, and rocks, substantially covers the entire enclosure. The vault enclosure includes a plurality of prefabricated panels formed from pultruded members having a plastic reinforced composition. The prefabricated panels, includes a plurality of bonded vertical panels, a floor panel attached to a lower end of the vertical panels; and a ceiling panel attached to an upper end of the vertical panels. The pultruded panels for constructing the vault enclosure include an outer planar sheet, an inner planar sheet and a plurality of support members that are spaced from each other. The support members are bonded or integrally connected between the inner sheet and the outer sheet so that the inner and outer sheets sandwich the support members. Each support member preferably includes opposing substantially planar surfaces for supporting the inner and outer sheets and a web member between the planner surface.