This is what I use (link to an older thread):
https://ogrforum.ogaugerr.com/...60#83790477270195160
I can now add that, if you pull the front side of the box out just a little, you can get postwar Lionel NW2 inside; likewise, one of the older Standard-O boxcars. And, if you cut a slot into the inner end flaps to accommodate the coupler, you can even squeeze in an MPC GP7.
These boxes have now made one move with me. I used some foam rubber in the ends of the individual boxes to immobilize their contents. I cut some cardboard to wrap around each of the "card houses" so the boxes did not slide out of them. They traveled just fine--though I should point out that I did my own moving, so they were handled with ample care.
