I made this a while ago and just posted a comment to "Harvey" about his version
I made a simpler one that just holds one Loco. Replaces the cardboard box. Box joint on 1/4" plywood. Made the box whole and then sliced it to make the cover. A couple small hinges and I intended to put a latch on and paint in road colors and decal with the road name and number. Cup pink foam (or blue) for a tight fit, and slice the bottom off, and then cut to fit the locomotive and glue the foam back together and slide in the box, soft foam in the cover. Very sturdy for travel.