I’m no expert, but I use rust to my advantage.
I personally use rust convertor to make it into a black primer.
My 2009 is not so bad. But I use liquid and spray convertor.
I try to get all the rust spots and larger under my vehicle.
Even did the rear axle rods which are now primer black since it had rust from end to end.
Nothing close to rusting through anything, and the normal rust near the brake components that’s usually there and other odd and end stuff I’m not to worried about.