Here is something I found that will hold passenger cars.
The only Tinplate passenger car that I own are the LCT 1695 3-car set. The box these came is was very large and each car was surrounded in enough Styrofoam that I could have dropped it off of a building and the cars would still be fine. A little exaggeration.
Here is the Styrofoam that surrounded just one car...
I am a diecast car collector and have plastic containers called Hot Cases. These hold Hot Wheels either in their blister pack or loose via foam inserts and are air tight. These cases are 16" x 15-1/2" x4-7/8" and have two built in dividers. Now, they run about $15 each...cheaper if you buy four or more I decided to try my 1695s in it. There was plenty of room to hold all three and still put 1" thick foam (purchased elsewhere) around the ends, top and bottom of each. Just needed to make cutouts for the couplers and carve indents for the trucks.
Here some photos...
