An illustrative example fuel cell manifold assembly includes a metal manifold pan. A polymer material liner that is self-supporting includes a primary wall situated adjacent an interior of the manifold pan. The liner has a channel around a periphery of the liner and a portion of the manifold is received in the channel. A reactant conduit adapter is received through respective openings in the manifold pan and the liner. The reactant conduit adaptor includes a flange that is received against an interior surface on the primary wall of the liner with an interface between the flange and the interior surface being sealed. Another portion of the reactant conduit adaptor is adjacent an exterior of the manifold pan that faces in an opposite direction from the interior surface on the primary wall.