Though I'm not sure the best material for making the gourd, keep in mind that it also needs to be strong enough to withstand the con. When I first went as Sango, I made my boomerang out of foam board. Although it was lightweight, it about came apart by the end of the con from it getting ran into by people. I had to completely remake it for the next con ^.^;; So learn from my mistake, if its a costume you plan on wearing to another con, make your props sturdy enough to survive the crowds!