My awnings were made using sunbrella. It is heavy, but I know it's gonna hold up, and it doesn't flog around in the wind nearly as much. If you sew pockets onto it, and cut PVC pipe to slide into the pockets, it will stabalize it even more and keep the edges a little higher off the deck, making it a little easier to get on and off the boat if your at the dock.
s/v Sol Mate - Pearson 367 Cutter
St Thomas, US Virgin Islands