How to save a stolen jet?

Ok guys, I found a solution that worked for me. I don't know if there are other ways but this one definitely works:

1. I completed the main story line.
2. I saw that I can buy the hangar in Los Santos, do that (marked as "2." on the map)! Note: If this is possible before completing the main story, the first point will be unnecessary.
3. Steal a jet from the military base (marked as "1." on the map). I used Franklin and his ability to slow down time during driving. Watch youtube videos on how to get away. I flew in a spiral-like way. Don't kill the guards, just drive past them, stop near a jet, go in and leave asap. I had to reload several times before I finally got the drift.
4. Bring it to your hangar.
5. Done, from now on you can destroy it and it will respawn there. I have no idea why the other hangars didn't work.

I found that with Trevor's second hangar, if you steal a fighter jet and park it as far back in the hangar as possible, then steals another and park it in front of that one then they both save and the one in the front respawns.