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West marine sells plastic rail clips that will support a 1 inch by 3/8 or so strips that creat a "bow" to have the rain run off. I think you could use something like that with a piece of canvas to creat a "dodger that would go over the bows and snap to your existing snaps. When using a rectagular piece of canvas it should be easy enough to make and will leave the bow and stern areas open. Here is a link:

http://www.westmarine.com/buy/taylor-made--bow-sockets-rail-mount--272781