I found that with deco model trucks, there are two places in the original design that allow mice unimpeded access to the header panel and headliner. Without some sort of baffle or "mouse guard", nothing stops mice from getting inside the cab. I fabricated a couple of simple structures that sealed off the openings and so far have had to unwanted vermin. Instead of steel wool, I use pieces of perforated sheet metal to block access through a-pillars and such. The perforated metal still allows the body to breath/drain and does not promote rust.
Cats work great but I have never been able to teach one how to discern mice from birds. Snakes are great too, I have a monster 7 foot king snake working in my shop...the only problem is that they only work part-time.
