I have bought coil zipper(s) in sizes #3 and #5. Either one is a good choice. The #3 is what you would expect with most camping equipment, imo. The #5 seems a bit heavy duty, which is cool if you like heavy duty looking stuff...
I usually sew some grosgrain across the ends to make the zipper non-separating, but that's just a strange quirk of mine...
"Civilization is the limitless multiplication of unnecessary necessities." - Mark Twain
“I go to nature to be soothed and healed, and to have my senses put in order.” - John Burroughs