I had/have the same problem. Keep the vents on recirculation when parked which will at least block access from the outside. I used one of those live traps once and never will again. The mouse died of heat, thirst and suffocation because I did not check it every day, or more often. I now use spring traps in my crawl space - easy, and quick. On an old Mazda truck I had to install a wire screen over the air inlet. Use that 1/4 x 1/4 or 1/2 x 1/2 galvanized.

92 Montero LS 3.0L V6 Auto, Stock, Original owner, 185,800K miles