I never did something like that, but maybe you can fix the center dowel somehow to the bottom and the top of your box like they do it with the “Cake Safe”. That would be fine for the bumpy roads.
https://www.youtube.com/watch?v=4WCajrmsQQ0
https://www.youtube.com/watch?v=75tYpaEqMRc
Floralilie Sugar Art
