Newer orphan coaches really are not a problem. Other than the cabinets and front/rear caps there is very little the end builder makes in their production facilities. Just about everything you can find from the same suppliers the builders used. Head lights, tail lights, fridge, tank sensors, leveling jacks, TV, furnace, air conditioner, water heater all made by someone else. Now if we're talking about a 25 year old coach everything changes.
But that said I would take the Tiffin unless the Gulfstream is heavily discounted.