I have travelled all over the world with my basses and my best advice to anyone is to get a fitted flightcase for your instrument. Best protection bar none, all wood and metal like. Expensive and heavy but worth it, a life time of protection on the road / in the air. Just pad it out a bit with nearest bubble wrap / rags if you're flying, just to make sure.
DON'T PADLOCK YOUR INSTRUMENT. I have had my basses opened multiple times by Customs (they usually leave a note in the case saying its been checked) And I wouldn't want to piss them off with the hassle of having to break your padlock.
If you have any catches or loose parts on the case make sure you go over them with gaffer tape, to create smooth edges that won't get caught on things. If you do a decent job it will also act as a deterrent to any sneaky baggage handlers that want a quick peak at your instrument too!
And of course make sure you give the instrument a decent downtune before flying to prevent any warping/neck breakages (though unlikely on well made instruments)
Example of last time I went flying with gear: