Why not make your own with canvas. Good quality marine grade all over ebay...Cut oversized a couple of inches, ask local seamstress to stitch a hem w nylon thread around the perimeter, add your own grommets and lace it. Look better and be better. The fiberglass I've seen at HD looked really brittle based on the number of damaged sheets. pvc foam is much lighter and holds grommets real well also and is available in 4x8 sheets.
Check these guys out for ideas - i found them a bit pricey...
http://www.alumapole.com/Merchant2/m...T&Store_Code=A
but I bet you can find an industrial plastics house around there where you can buy the same stuff for much less...