Peeked in with my flashlight and mirror and the front pads show what I would guess is half a pad left. Rig has 53K miles. Original pads as far as I know, purchased rig with 19K on it.
This may or may not help but I have the complete service records for my Former Rental and every time it was serviced after a rental and before the next one one of the many things that were checked was the brake wear and it was recorded.
Their criteria before sale was if they were 50% or less they were replaced,my records show that they were replaced at 56293 miles and again at 86560 miles,when I purchased the RV it had 91000 miles on it.