Were they as a result of damage by the same rock letting water into the steel braces on the adjacent tyre causing rusting and delayed failure? The worst damage on modern trucks is usually fronts blowing the air filter housing to pieces.Yeah I've had two rear failures both during the summer when exhibiting at vintage rallies, the first as you say had a rock trapped between the tyres and blew out travelling along the road on the o/s/r, couple of years later on the same side while parked up at the rally field (having been parked for over 40 hrs) suffered a blow out on the o/s/r again my poor friends in the next door caravan got a fright as they were sitting outside enjoying a cup of tea in the sunshine (tea went everywhere as you can imagine) the blow out split a huge chunk out of the brake hub.