i personally am a fan of kata and lowepro. for my big UW rig, i use a kata 195 (its c-195 or cc-195 something like that). its designed for large video cameras but perfectly fits a UW rig, with the housing and dome port upright, not flat, making the most efficient use of space. its also carry on size just barely (i once had someone at security question it, but a more senior person then said it was ok). you can also get this little kata dolly that fits in it to wheel it around. works nicely. very hard and solid for a 'soft' case.
last time i travelled i fit a housing (no handles, those went in checked luggage), 9.25" dome upright, macro port, 2 inon strobes, 2 dive computers, large viewfinder, external hard drive and a heafty nikon 300/2.8 lens. my 2 bodies & lenses went in a smaller 'personal item' sized bag. kata does make really solid stuff. lowepro is good too. cheers,
chris