After I have lowered my car I have bottomed out a few times. Now there is one position (the jacking point) is rusting because some of the paint is gone..... So what do I need to do to solve this problem? Thanks.
Rhino Liner is more like a spray on crazy plastic.
The paint used for undercoating is almost like a goopy tar. You can buy it from stores, usually just called undercoating.
I'd follow EB's steps. Sand (every piece of rust)
Prime with rustoleum to stop further rust
Top with a few layers of undercoat paint.