PVC fabric for small inflatable catamaran hulls?

I'm on my way to make a small catamaran for padling and rowing.

What is the most suitable quality, weight, density and thickness of PVC fabric to weld inflatable pontoons around 15feet range?

 

Check out a whitewater rafting supply outfit. Whatever thickness their fabrics are will likely be more than adequate for your requirements.

 

I have contacted a few stores and inflatable producers, but have not received any response yet.
I suspect PVC used in whitewater rafts might be overkill for a small catamaran for flatwater use. It good if I can keep the cost down. I'm planning to do reinforcement strips on the bottoms, out of whats left after cutting out the tapered cylindrical hullshape.

 

these guys sell what you need in small quantities. might be cheaper to find a local supplier, but I am sure they would ship overseas.

http://www.seattlefabrics.com/products.html

 

PVC is difficult to weld unless you have the proper welding machine, Hypalon and glue seems a better choice to me.