I did something different altogether.
I bought the soft foam style cowl seal and glued it to the bottom of the vent door, just inside the lip instead of the cowl. The lip on the cowl engages the foam seal more securely than how the bottom edge of the vent door engages the seal. I did have to cut the foam seal and glue the ends back together so it will fit inside of the lip under the vent door. That foam is easy enough to glue with weatherstrip adhesive. No leaks, even when sprayed with hose.
