Body filler in the trunk?

saw a 442 olds that took top honours at a high end car show and the magazine article outlining it's restoration.There was hardly anywhere on that car that wasn't covered with filler..including the body,floorpans,frame,trunk...you name it.The frame was pitted beyond belief...but looked mint when finished.
..if it's just a skim covered with quality paint and a trunk liner you'll be fine.