filling firewall with sealer

i just ran my power wire through my firewall today on my 98 civic si.
through the spot under my glove compartment through a rubber closed opening. i cut a little hole in the rubber. stuck my wire through....and then ran it through my car.
now my questions is : should i use a expandable foam or sealer just to put around the opening where my wire goes through the rubber. i mean its pretty clean cut, but jst to be safe so no DRAFT or moisture comes through is there anything i just put on to seal it...if so ..what works best
thanks everyone