I don’t think it was as much of a heat issue as it was the selection of the wrong materials by Prevost when the coach was built.
My coach, like everyone else’s, has a lot of plastic, rubber, vinyl, and other materials in the engine area, and they’re not hardening and cracking like these hoses. Mine snapped like a dried twig at the header tank, which is actually the area in the engine compartment that gets better ventilation from the radiator fan.