Hi Steve, if going that route, I would section it in with either an overlap or buttweld at the spot welds that run across that hold the trunk floor to the valance. You can hide it nicely with testefully done seam sealer there no body filler needed and the bumper will hide it. You dont really have to remove the taillight housing "buckets" sheetmetal to swap the whole pan, but since you dont need to go that far into the car anyways, then I understand doing the non stock seam. If mine wasnt as bad all around as it is, I would be putting a non stock seam right on that trunk floor spot weld line.
