I used something like Kurt did. But the foam sealing tape I got expands a BUNCH. I have a couple, don't remember which I used there, but they come off the roll about 1/8-1/4" thick and expand to 1" or 2" (depending on which it is) in a short time. Used the same to seal top of the radiator to the nose (to force the air through the radiator) and to seal firewall to the body.