Need Help/Advise Body Mount Replacement

[Mr Banshee]

Began doing a body mount replacement. Found that my mounting on the rear sill and rear bed floor is badly rusted out. I'm in the process to remove the rear cross sill to fabricate a new sill with the mounting pads. I found when removing the spot welds and lower bolts that the inner structure behind the tail lamp that the rear cross sill bolts to is completely rotted out. I was looking for a patch panel of some sort for this but all I found was the tail lamp rear corner sheet metal for the outside. I know I need to remove the outer bedside (quarter panel) to repair this. Does anyone know of a repair patch panel available or have some insight how to repair this piece of structure? I can post some pictures of what exactly I'm talking about if need be. Thanks Mike