Cowl Vent Grille And Rain

We had some really heavy rain the last few days here and while driving home, I noticed a waterfall coming from behind my glovebox. After some research, I removed the cowl vent grille and looked inside. I saw a pretty good size rust hole just below where the air intake enters the car. I was considering spraying some flex seal stuff on it, but I think the hole is to big. So, since I don't have a/c and my vents don't blow air anyways, can I just put something over the holes that the grille covers and place the grille back on, or does this area serve another purpose besides for the a/c and vents? Or would i be better to tape the rust hole up and then spray the canned sealer over the tape to seal it? Thanks

Thanks for the reply. It appears that raised portion is what has rusted. I can tell the area is raised to prevent water from entering the factory placed airhole, but the rust has put a hole in the front of that raised area, so the water just pours in. From further inspection, it appears the only way to reach the hole is with quite a bit of disassembly, as just taking the grille off wont let me reach the whole hole. So looks like I will seal the area under the vent grille for now, and add this to my list of things to fix the right way once I move to my house with a garage.