If you are talking about the sheet metal above the cab corners, you won't have much access. It might be easier to access the cab corners, but you will have no more access than you already have by going underneath the suburban. I think the area that you want to access is sealed next to the sill. Rob took a picture of my suburban parts truck that I parted out years ago. It shows this area after I cut the sides off to expose the inside interior wall between the exterior sheetmetal.
