I came across this tutorial a while ago and thought I would have ago.
The first one isnt quit right as I left the staples in the end of the zip which made it difficult to sew up the side seams.
The second one turned out much better. (click on the thumbnails for a bigger photo)
I lined them with a wipe able fabric I bought off the Internet from here
They are easy to make, so I will be making some more.