When I was a kid we used to let the dog ride in the back of the estate car. She would sometimes try to lie on top of a suitcase and then slide off on corners. Dogs won't always realise they are doing things the hard way, but if it doesn't hurt them it can be okay. Enjoy your road trips.
!BEER
Lol
Yeah sometimes whatever works for them is the best solution. Funny as she used to lie down on road trips but now does the ol standing routine