Replacing the bottom panel in the cab over of my 2005 Hawk. Planning on using marine grade plywood since there are no voids in it, will be using either 1/2" or 5/8", haven't removed it as yet so not exactly sure what thickness is original. Thought about using HDPE but it's heavy and would sag across that span. If anyone has a better recommendation on my material selection please chime in. A stiff no rot composite would be best but I want to keep the cost reasonable.