I have a Bob Allen take-down case designed for an auto with two barrels. It's heavily padded and has served me well. Unfortunately it's no longer listed in their catalog. I also have a collection of attractively priced Ace Case pistol rugs and tactical rifle cases. Ace has break-down shotgun cases in
fabric ($25.90) and
nylon ($29.40).
Like most take down-cases, the Ace is 10 x 36-inches which is a little long for most O/Us. If I recall correctly, in the past, they were willing to cut it to size if ordered directly.