Well I will start the ten pages off then!! 
I was told (rightly or wrongly?) that legislation decreed that the driver had to spend his rest period away from either the steering wheel or the whole vehicle? None of the drivers from the fifties and sixties that I knew slept in their cabs, even into the 1970’s they lodged out and when I did my HGV training in 1976 the digs I stayed in at Pickering had many drivers staying there overnight instead of sleeping in their cabs to save the night out money. So no real call for factory built sleeper cabs back then, although some of our Foden eight legger tippers at Tilcon in the early eighties were fitted with drop down Jennings bunks for the lads doing distance work and a couple of Foden Haulmaster tankers on Y reg had factory built double cabs although the drivers didn’t actually night out!
Pete.