What do you want to carry? I’m wondering whether it might need an internal frame to stop it flopping to one side or the other, and to stop it drooping Dali-like over the tubes. But I think it would depend on the contents.
If it is just for you and you’re never going to carry more than a waterproof, tube and tyre levers, there’s no need. But if you want to be able to pick up milk and wine on the way home, you might need some reinforcement?
But it might be something you could make retrospectively.