I think the best thing you can do is get a Crate

 I think the best thing you can do is get a Crate, and leave him in this to Travel In. Not only will he be Safe, but you can also Place Puppy Pads in the Crate so he can Safely go to the Toilet. When you Stop you can also place Food and Water in some Small Non Spill Bowls. The main thing is to keep him Safe and make sure he does Not Escape. You can take some measurements and see what Size Crate you can get away with. Good Luck.

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