http://uk.ask.com/question/waterproof-spray-for-paper
as we all know paper when wet krinkles up and gets all soft an mushy… If this spray works on a piece of paper, it should work on a shamisen dont you think?
Its a type of leather for the kawa, and having an extra bit of safety on there would be awesome ^^ Not sure if anyone has tried any sprays or gels for the kawa. But if you do please post results or share your experience 
I am very nerveous about bringing my shamisen out an about for some in town playing, as englands weather is unpredictable and can rain at any minute really, I would really like to get my hands on a spray that wont damage or cause the kawahari to pop off.