As a kid in the early 80s, doing 12 to 16 hour explorer ticket bashes on mostly NBC vehicles, the attraction was simple-heat!
Anybody that regularly used Bristol VRs, early Leyland Olympians and Nationals knew to sit near the back by the the engine and well away from the front doors if you wanted to stay thawed out for the 8 cooler months of the year.
ECW Olympians in particular often used to have lovely blast of warm (if sometimes somewhat sooty) blast of air coming out of the gap between the nearside rear armrest and back seat cushion. Very cosy on a winters day
On many VRs the only source of downstairs heating was through a grille at foot level below the back seat- toasty toes guaranteed but sometimes spoilt by the draughts from the emergency exit.
If you got an RE or an LH and the month had more than 4 letters in it you had no hope- even for a youngster they were freezing cold in winter- it must have been horrendous for the elderly etc!