I am looking at a Ranger to buy, 2002, the main frame looks completely rust free and in great shape. But between the frame and the outside of the car, there is another frame like rail, shaped like a L, then seems to run kind of where the floorboards would be (above it), and a couple sections of that have significant rust (I was able to pull a a quarter size piece of it clean off with my fingers). I don't know what this smaller "skirt frame" thing is, and should I be concerned if it is rusty? I checked everywhere else on the car and that is the only area of significant rust I could find.

The area I pulled off had a crimp end of what I image was some sort of grounding screw attached to it, if that helps identify what it is

 

A pic or two would help?

 

It was at a dealership, and I've been looking online but cant find a picture of the underside of a 2002 Ford Ranger to point out the area I am talking about