The problem of hook and elastic pannier mounts was solved by Rixen and Kaul, Orleib, Arkel etc in the 1990s. Locking, quick-release pannier mounts are far safer and more reliable than any other system inc straps, buckles, velcro whatever.

You can retrofit R&K mounts if you have a tough stiffening material (such as Coroplast). You rivet the rail on and slide the hooks onto the rail.
Good quality systems are simple, reliable and tough, they never fail and when they do, they fail-safe. Poor copies are complicated and fail in a manner which dumps your pannier off the rack when the lock snaps.

This is the best illustration of R&K mounts but they can be mounted to anything.