Haha, the two chessies I knew were often in their owner's car (she was a dog walker that walked my EX bosses dog, so in decent weather she'd just bring her dogs as she drove around to clients and let them chill in there). As far as I know they were typically standoffish chessies, but reasonably friendly....not aggressive or anything, just a little wary.
Accidentally walking too close to her truck was the most terrifying thing. They wanted to tear limb-from-limb anyone who got too close to their vehicle. They'd body slam the inside of the car, too, so on top of the snarling and roaring you'd see the car rocking and hear them banging around.