@BART:
Gotta say I agree with Vicki, life's too short to worry about "what if's". Just look at the face of the next dog you see hanging his/her head out the window of a moving vehicle. They always look so-o-o happy! My previous boy absolutely hated to get wet - period, unless we were in the car. Stuck his head out the window every time regardless of the weather. Had a regular vet appointment once during a "time to start building the ark" kinda downpour….showed up at the vet with a completely soaked head and completely dry body:).
When you have seen an animal thrown though a window because the driver had to stop fast or was hit by another car, when you read stories like the woman in San Jose who had her pup riding on her lap, was in traffic and got into an altercation with another drive that turned to road rage and had the dog yanked from her lap and thrown into oncoming traffice and killed, or had a pet get thrown from a vehicle because the doors opened in an accident and runs off…. then many might think twice about restraining... And as far as windows go, ask your Vet about eye problems from dogs hanging their heads out windows...
Regardless if a car or semi... RV or SUV... pets should be restained when moving... there are a number of different kinds, my preference is a crate (which by the way is secured as not to roll around if an accident did happen)...
As they say to each their own...