A method of manufacturing a closed, hollow toroidal structure having a rigid internal annular plate includes treating one annular surface of the plate with a release coating, applying to the other annular surface of the plate an adhesion promoting coating and positioning the plate within a mold having a generally toroidal internal cavity. Next, a fluid conduit is juxtaposed partially within the internal cavity of the mold adjacent to the annular plate and partially outside the internal cavity of the mold. The mold cavity is then filled with an elastomer followed by curing under heat and pressure.