I have my EPL2 underwater gear in an Underwater Kinetics hard case (the largest one that meets the carry on dimension limitations) with the pluck foam insert. It holds the housing (Olympus) with the Zen port mounted, the stardard port, a Subsee +5 lens and the mount for the flat port, two Inon S2000 strobes and fibre optic cables, two LaLuz lights, and the various arms and connectors for the strobes and video lights, my two page laminated assembly protocol, some various odds and ends light silicone grease, extra O rings etc. The whole rig, without the camera and lenses, which I take on as my personal item, weighs about 18 lbs and fits under the seat ahead of me. It is well cushioned and can take some dings and drops. If necessary I can put the camer in the housing and take the whole rig to the dive boat. However, I normally assemble everything in my hotel room and take it to the dive boat.
I have the yellow case and have put DAN stickers all over it. Most people thing it is an oxygen kit rather than camera gear which suits me.