I'd agree that ripstop is not the best awning material.. but for a lightweight sunshade regular sunbrella might be a bit heavy. The [problem with a nylon awning is that it will have a lot of stretch and little stability in any kind of breeze.
Down in the Caribbean our friends use a material that resembled Sunbrella but was about half the weight.. sorry I don't know the tradename of the stuff but something like that is available I'm sure (they had theirs made by a sailmaker in Guadaloupe)
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)