[John-eh]

I've learned, by my own experience, that severe rust on the rocker panels doesn't affect the stability of the focus, as long as the door sills remain rust free. The rear suspension mounting point is high enough up inside the underbody not to be affected by rusted out rockers.
That stick on wall molding, used for bottom of walls at floor level, comes in rolls and makes for a good bolt on cover over for rusted out rockers on a focus. And it doesn't rust.
I recommend Rustcheck spray over rust to stop more rust from happening. But needs to be done twice a year on real rust, not once. Don't expect any guarantee at this point from Rustcheck. ha ha. But it works.