After owning a 2008 FJ Cruiser, a 2015 4Runner Trail, I learned that there are certain rust areas to watch for.
One recommendation: Next time you take your skid plates off, make sure to put anti-seize on the bolts.
Mt last 2 Toyota's had seized skid plate bolts. If fact, I will be adding anti-seize to my 2020 skid plate bolts.
Not sure why but Toyota still does not take corrosion seriously.
You would think that after having to replace entire frames on the other models, they would make more of an effort.
Like I always say, rust is the only thing that can kill Toyota.