You should never, ever, travel by air with a sealed up housing, forget about o-ring, but you could easily pop a window or unseat a port lens from it seal, manufacturer don't write that stuff in the manual just for making your life miserable, we know what can and does happen, trust your manufacturer and stick to their recommendation.
if you are adamant about keeping the port attached to the housing, at least remove the eyepiece if possible or the main O-ring (Tip: put a thin piece of plastic from a soft drink bottle of something similar between the fron and back as a flag to remind you that there is no O-ring in the groove, heck you sure don't want to forget that O-ring!!!
