Achilles always like to ride shotgun as soon as I open the car door, and I usually let him when I take him to the park, its literally a block away; however, he knows he's riding in his crate for longer trips. :D
FYI___ My daughter had her dog on the floor board of the car while driving to my house when she noticed CoCo was panting quite a bit, She quickly turned her AC to the floor and she cooled down. The reason I am posting this is to save your animals from heat stroke. Lone Star Bulldog rescue posted where a bulldog that just got adopted had passed away on there way home...Most cars does not have vents in the back seat. I think if the ac is blowing at the back or at the floorboard might help....Maybe a portable battery operated fan that clips on may also help...