@mike, a thought.
We see a lot of those big stripey nylon bags that are equivalent to a suitcase. I am pretty sure that they are produced by small backstreet guys.
If you can find a guy in Luosiwan that sells them (and other shopping bags) you might be in with a chance of finding a manufacturer, or the supplier, and you may be able to follow the supply chain.

@Tigertiger.
I think you are reffering to the blue/white /red stripey which half the train or bus users have? That material is Jute and wont last a season in the sun.
I'm looking for the kind of material they manufacture backpacks and russacks, a brand name is cordura but thats overboard.
It doesnt need to be waterproof as i would like it to breathe so the sails can dry...
Obviously the military canvas would be ok but it retains water and will Mildew.
A heavy duty, tightly woven net or mesh would suffice.
Any long plastic zippers, 2 m? I can also use velcro which is available in rolls.

Zippers and velcro, pretty sure there are shops. Some sell stuff like that also accesories in their fabric shop or can give another store a call they know has it.
Or just go to taobao.
Don't go for the colored clothing bag kind of woven plastic. I think it will deteriorate fast in the sun. Plus it's a bit too water-tight for your needs.