Assuming you are referring to the chassis engine's alternator, and you have a NON-turbo 6.2L diesel, AND ASSUMING the engine has the same alternator mount and accessories as pickups and surburbans, I picked a '92 surburban and punched it in and got this.
6.2L accessory belt
This is for engines WITHOUT a vacuum pump to operate a brake booster, in other words, you have hydro-boost brakes operated by the power steering pump.
Now, if you are referring to the 120v AC generator used to power the electrical receptacles in the coach, some generators (Generac I think) did use a belt between the motor and the generator, and this I cannot help you with at all.
Charles