The fresh air intake for your HVAC is where you suspect it is, under the cowling. Simply remove the blower then look up to the "light"

If you suspect that is the ingress, simply put your HVAC into recirc mode before shutting down. That's the flap that blocks of any fresh air intake.
I've tried covering this fresh air intake hole with chicken wire but I don't think it worked as I catch inside the 80 frequently. The ratzapper works real well but they still stink up the inside
Also, check the square hole in the body, WAY in the rear, under the cargo area. They should be covered with plastic covers but one of mine fell off and this allowed a giant rat to go into my 80.
Another hole I closed up is at the firewall where the main ECU harness goes through. They ate through the rubber grommet and made it inside.
Still looking for more egress holes.....