I've only traveled with my gun once (last month), so I'm no expert...
I bought a solid pistol case with two lock points, two Masterlocks locking it.
Place in my suitcase, I don't put locks on my checked suitcases as I never put anything valuable in them, that stuff (computer, camera, etc) comes with me in my carry on).
I also had print outs of the TSA policy, and the Airline policy on me.
Declared at check in, filled out the tag, plopped in the suitcase on top of the gun case, the end. Coming home, they walked me down to TSA scanning station, scan, "have a safe trip", the end.
I DID notice a TSA inspected white tape on the back of my suitcase when I arrived home.
As to don't ever do this because you'll go to jail if you get diverted to an anti-state airport. I'm no lawyer but... if you are smart enough to know the regulations to do this at all, then be smart enough to not take possession of said luggage from the airline in the anti-state airport. Just tell them you have a declared firearm in it, and it is on them to get it to where you are going, have a nice day. If it ends up an a baggage carousel, go straight to the missing baggage desk, and get in front of the issue, and have them take it off the carousel. This is how I would handle it anyway, and I won't be going to jail.