No way, kids are not allowed to ride back there. About 20 years ago, a woman had seven kids in the bed of the pickup here in town and got into an accident at under 35mph. Many of the kids died.
Your dog has even less weight than a lot of kids, he will go flying and end up broken, possibly run over by another vehicle. Why, why, why chance it??? Because it looks kool???
Sorry, but it is one of the most irresponsible things someone can do with their kids or dogs. Your husband may be the best driver in the world, but that doesn't stop the high school student from pulling out in front of him. And a minor injury can mean death or disfigurment of your best buddy.
And another thing is that we all assume that our dog will know exactly what to do if someone foolishly walks up to his truck to pet him. Oh he wouldn't hurt a flea. BS! We do not know what he might smell on some fool that makes him react. And what about kids? Dogs are an attractive nuisance. If a child walks up to pet the doggy, the doggy might not realize the child is ok. Why risk a possible incident with your beloved companion? Why risk a bite on our breed and euthanasia for your pet? To be kool??? I cannot think of another reason.
Sorry, but this is one of my pet peeves -- obviously. I love our breed and am absolutely disgusted when something so foreseeable happens.