Had a 93 Pace Arrow Diesel pusher for 12 years. All I did to winterize was open all faucets, the pressure relief on the HWH and opened the drain valves in the water compartment. All water would drain out of the lines AND the HWH. I only used the pink stuff in the traps. Worked w/o issue for 12 years.
The Hot water heater's cold water in line must have dropped down to the bottom of the HWH & would siphon the water out while draining. Was kinda funny to pull the drain plug & have just about a 1/4 cup of water leak out.
I did NOT have a washer/dryer in that rig. Don't forget the hoses & such behind them.