Most luggage locks are very standard. So standard that there's very few key combinations. Airport thieves carry keys that will fit nearly all the luggage out there. You greatly increase your security by using an additional lock, like a small padlock. A small padlock presents an obstacle that will take a thief more time to get in. Luggage isn't exactly a "hard target", but the basic idea of slowing a thief down is still effective. A large number of travelers use personal locks, so having one on your luggage doesn't identify it as being a more valuable target.
If you use a gun case, then you've pretty much identified the contents and increased your risk. Use a container if you can that doesn't look like a gun case. Normal hardside luggage that can be locked with a padlock is great for handguns. I've used a small footlocker for rifles that fold, collapse, or breakdown (like FAL, AR, etc). For longer rifles, look into those long tube-like cases that are used for shipping trade-show stuff. Sorta like those golf-club travel bags in size, but for trade-shows. They look like a short sonobouy container made of stronger stuff. There's companies in every area that custom make these. There are production line cases of standard sizes available as well, usually from the same display vendors. Get one long enough to hold your rifle. Put a bunch of different trade-show stickers and suff on it. Throw it around a bunch to make it looked used. There's very few thieves that will take the time to open a trade-show case to see what's in there, when they can be prying open that Pelican next to it.
Ross