How much rust to replace frame?

Got my recall letter on the frame. Looking at it yesterday, I do have rust on the frame and leaf springs. Even though I live in South Texas, I've done a lot of driving up north and my ride has seen some salt.
My question is, how much rust are they saying is enough to replace the frame and or leaf springs? I realize that is a subjective question, but my frame and springs seem to be structurally sound, just a little rusty.
Thanks

 

I believe there has to be a perforation for frame replacement, someone can correct me if that's not correct. Look at the boxed section of the frame by the cats, that usually where most of the perforations are happening.

 

Frame has to have perforation I belive size of dime but excessive rust may require them to spray a rust prevention to frame.. Kind of covers the problem but supposedly stops it from future rot or rust .. Look at my avatar I'm a new frame candidate but this is excessive. .

 

And yes Skywalker is correct cat area is a known problem area but not limited to.. Cat area of my frame was affected badly

 

It's not about 'surface' rust.... It's all about perforation (rusts from inside out). I thought my frame was pretty damn good..... but there was a 'soft spot' in the area under the drivers side door. That's where the perforation is the worst on most of these trucks.

During inspection, they poked a hole right thru that 'soft spot' and created a hole about 2.5" x 1.5". FAIL.

Check the inside of your frame around the area just forward of your drivers side door. If there are any spots that feel 'soft' to the touch.....you could possibly have a bad frame.

I truly thought my frame was good....but.....one little spot failed it. Granted...after finding that one spot, they never inspected the rest of the truck.