Well I went camping recently and my brothers greyhound was crying to get in the car and spent hours in it by choice. ( don't worry, we were huddled round a campfire next to the car, or in tents next to the car) if you left the door open he was unhappy with the draft!
Over the course of the weekend his dog would want to be in the car whenever we were at the campsite. He was fine whether he could see us or not. My dog would have whined if he was in the car and could see us. However I've left him up to 4 hours when I park the car outside friends houses where he can't come in. If I can't see the car from the window of the room I'm in, I won't leave him more than 10 mins. But if I can see him and he's settled how's it different to being in a crate....
I do live in the UK, so no crazy hot weather, and I wouldn't do it on a hot day. But I am certain he likes joint me on errands.
To be honest the main reason I don't leave him in the car is because people are crazy and try to rescue him.
Genuine interaction "Park car near pharmacy, go in, can see dog and car from window.... Lady walks up to my car, does exaggerated look around, makes phonecall.... I'm being served so put in my order before walking to the lady....lady starts talking about how it's terrible, the dogs been there hours, she's called the police... I say it's my dog, I've been precisely 16 mins, it's cloudy and we ( me and the lady) are both wearing coats... She rambles on about the car heating up more than outside (which is true in hot weather, but it's cool enough for us both to be in coats, and the windows are wide open as the dogs in the boot which has bars), besides, as we can both clearly see, the dog is fine... Anyway, I let him out for a pee, give him some treats, he ignored the puddle I pointed to for him to drink, and happily jumps in the boot again... I go into the pharmacy to collect my prescription and see the lady come back and the police arrive. Anyway, I stay in the pharmacy till i'm done, walk passed them, get in the car and drive off. I can only assume the copper could see my dog was fine. But if she's willing to call the police, someone will smash with window.
Yes, he's panting... He's excited because your interacting with him... Move away from the car and I can bet money he's just looking in the direction I disappeared from!