Duster cardboard sail panels

my were warpped bad, but all there on my 72 swinger. i took a spray bottle, wet then over and over again. came back later and wet them again, and again, when they were limber, i layed them on my black top driveway when it was 99 degrees and placed floor tiles over them and then placed tool boxes, bricks etc. left them all day, brought them in that night and then did it again the next day. they are perfect, i then used some fiberglas on the inside where the points are to make it a little stronger and not break them off. and they are perfect. if a corner is gone the fiberglass might help. the issue is the small cardboard holder of the plastic pin that you knock in on the back side and where it is positioned. if you can mimick that then you can use anything almost for the boards. good luck here is a pic you can see the small glue on that holds the knock in plastic pin, and then a thin layer of fiberglass such as the corner of the top pic. tks Mike