You don't drive motorhome in city traffic all the time, so why brakes should wear out fast?
I routinely do 100,000 miles on brakes in cars, so am not worry about mh brakes for long time.
Coming to serpentine belt, those can last 200,000 miles in cars as well, but YMMV depends on the brand. In motorhome belts work harder, but they are also bigger.
Beware about different belts qualities.
Had incident on Mercedes, where not likely original belt at 290,000 miles had cracks. I put new belt and that one become bundle of strings 3 days later, so the old belt with cracks went back for some time.
