I recommend not to, when the camera is inside the housing it is tighly fitted, that mean any impact is directly to the camera body and trust me a camera is way more fragile than a housing, the other thing is that in this scenario, should TSA drop your luggage (and they will) if something external is in contact with a push button or lever , it might push this button or lever and internally the impact will be transmitted straigh to the controls. now theses controls are meant to be pushed gently with finger, not impacted by a metal shaft... I do like Deep6, stuff it with gidzillion stuff like batteries, charger, close up lens, sync cords, denture, fake eyeball and spare kidney (I do like to party).
I have been in this industry since 1990 and have seen my share of housings, not only as a underwater photographer, but as part of my work at Aquatica, and yes I have seen this kind of damage, and yes that is why this is mentionned in the owner manual of the housing. BTW, A lot of the stuff that eventually end up in the owners manual of a product is based on actual event, such as little gems in the Nikonos manual that said something like, do not open back door of camera while camera is submerged and my favorite about not changing lens underwater on the Nikonos. Both likely would put a wry smile on most of us, but I actually had both situation show up at my camera repair shop in the 80's, the worst is that both still tought that Nikon should have written << DO NOT OPEN UNDERWATER >> on the door or /and the lens and therefore were the party fully responsible for their predicament. Man did I ever learn a lot of thing about the low side of human nature in thoses 10 years as a camera repair technician
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As a rule, If I travel any distance I won't even transport the camera body with a lens attached to it, been there already, pulling out a camera body with out any front and its innard exposed is a sobering experience, the longer the lens the more leverage it has.