I think I got the idea from you, I think you commented that you did that to make your panniers something you could carry onto the train. In my case I did it to make four items become one to meet the checked baggage requirements. I bought a mesh duffel for that purpose.

That said, when I took a ferry and had to carry everything onto the ship, it was easier to carry two panniers in each hand, handlebar bag with a shoulder strap. In that case, ship's crew handled our bikes.