You can sew the open end closed. Just use an overcast stitch by hand.
Hmm, Now there's an idea! Old timer brain forgets... I used to do this with regular bulk coil zipper for many projects but wasn't concerned with water resistance, I guess I could do the same here, and seal the stitching. Do you know if the zipper material adheres to seam grip or something like it?
Loc: Pittsburgh, Pa, USA
You can also find them at JoAnn Fabrics, one in your area could save S&H.
Life should not be a journey to the grave with the intent of arriving safely in a well preserved body, but to skid in broadside, thoroughly used up, worn out, and loudly proclaiming Wow! What a Ride!