I use a Pelican 1510 roller carry-on. It's heavy af when loaded (+/- 42 pounds) but looks compact. I've never been challenged at check in. I was asked to gate-check it one time, but only because there was a shortage of overhead space. I figure worst case, if I do have to check it, I am comfortable in doing so.
The case fits this mess of stuff (barely)
* Aquatica housing with D7000 body inside
* handles for above
* two Ike D161s
* three lenses (105, 60, 10-17)
* wet diopter and holder
* flat port
* two extension rings
* two Aquatica arms and "joints"
* 45° viewfinder
* two strobe chords
* one Ike charger, one Nikon charger
* spare o-ring sets
* misc tools, swabs, lube etc
I pack my mini-dome in a backpack with a spare D7000. 8" port gets packed with clothes (it's acrylic), as well as additional Ike charger, focus light etc.
So basically, all of this crap, less the ports and one body fits into it.