That pic from 71Charger explains to me the construction . I now realize it is the rear section of the rocker that is rotted out. It looked like there was a joint in the rocker where I cut it out but now see it was one continuous member. I restored this Texas car back in 2006 and it was pretty much rust free, except for the trunk where water had been sitting and these are the only 2 areas that have rusted since then. The frame rails and everything else have not deteriorated. The cause of the rot is my fault. Someone (me) sandblasted the trunk back in 2006 and that's what created this problem. Sand had filled the areas and any water that got down there, probably from washing the car and any leakage around the rear window seals was retained by the sand (garnet blasting media) and caused the rust. The rockers toward the front are still solid. I'm thinking about buying one rocker, cutting it in half and doing a splice job on the rockers. This is not a show car and I don't plan to sell it. My son and I do all our own work, so taking to a shop for a professional to do the job is not part of the equation.
Any feedback is appreciated and taken without offense,