Strips cut from an old bicycle inner tube make a great gasket for metal sheets that don't quite seal up, prevents chafing squeaks & rattles. Pop-rivets with a small washer holds it pretty well.
This is also a good time to examine the radiator/bulkhead area for air leaks - all air must go through the radiator core, so plug all extra access, wiring pass-throughs, lights not used, bolt holes etc. The hood must seal to the radiator support top when closed.
