It sounds like you have gotten hold of one of the "Infamous" Coleman ABS one-piece roofs. They had a terrible problem with "sag" in the center and on the sides. I had a '98 coleman Natchez and was on the third new roof when I sold it in 2001. Second and third roof had the roof brace (for the weight of the air unit they claimed) and it still sagged. The 12' boxes had a much more prevelant problem with this than did the 10' boxes.