Is this you first I/O? If not winterization of the engine is no different. The fresh water system should be drained by running all the water out of the tank then running pink antifreeze through the system until it comes out all faucets. Have the holding tank pumped empty and pour antifreeze into the toilet and pump it through the system.
1997 2400 SCR
5.7 Vortec / Bravo 2