method and apparatus for rotationally casting a plastic tank liner having a molded - in access fitting and for ensuring a uniform thickness of plastic in the wall of the liner and on the fitting . a hollow mold having a mold cavity surface conforming to the surface of the liner is provided . an access fitting is removeably mounted on the mold so that the interior surface of the fitting may be coated with the molding plastic and so that the molded liner and the filling may be removed from the mold as a unit . the mold is rotated about orthogonal axes while the mold is heated to a resin liquifying temperature . additional heat is supplied to the fitting at a rate proportional to the mass of the fitting so that the temperature of the inside surface of the fitting is increased at a rate substantially corresponding to the inside surface temperature of the mold .