Just bought a new to me 2017 LX570. This is the nicest and most expensive car I've ever owned and I want to keep it until the wheels fall off. My 2008 4Runner has almost 300,000 miles and it's very rusty from all the salt that Chicago and IDOT throw on the ground. Would frequent car washes with undercarriage spray be just as effective as fluid film or another protective coating? Or should I just bite the bullet and coat the undercarriage to prevent the rust cancer from devouring my nice car?