A modular casket made of lightweight materials is structurally reinforced using a structural sealant along at least the inner surfaces of the side panels, and optionally along at least side edge portions of a base panel to which the side panels are coupled, to stiffen and rigidize the casket against flexion along longitudinal and lateral axes, as well as torsional flexion. The structurally reinforced casket is sealed or more readily sealed against leakage and provides other benefits of structural stiffness and rigidity with relatively small cost and weight penalties.