Most times the bigger teeth zippers are cheap to tear out of thrift store bags. I don't care about the bag so I rip it out.
I needed several duffel bags for a kids camp so I made the one yard tote bag but made it long and wide. Added the zipper and webbing around for the handles. Boxed the ends and was done in a flash. The kids are still using them for overnight bags. I like making bags, they are always useful and well received.