There's a reason for sleeping in the boot
He would have chosen the boot in order to avoid the risk of getting bothered by passing police officers - since the act of being inside the car and in possession of the keys may leave you liable to prosecution (don't ask me why - it's just what I've been told)
Plus also you get a better night's sleep without passers by tapping on the window to ask "are you OK?" or (worse still) reporting to the authorities their concerns about "some bloke out cold in the back of a car".