We had a guy used to carry a newspaper with him, at nap time he'd spread it on the floor, which was quite roomy at the time since we had long nose tractors so no doghouse and just one seat. He was running from Tannersville Pa to Hartford Conn, a 5 hour run, when he didn't show up in 10 hours they had the cops out looking for him, found him sound asleep on the floor in a rest area.
Let me show you my hammock strung from the driver's door mirror, over the door to the passenger door. Open window, hold rope, slam door. Zzz!