All the brand new RVs I hauled to dealers held together well.
As to the weather, a strong El Nino will be your friend. Many good suggestions above. My choice too would be to stay on I-5 to Portland then East on I-84, as it seems to be a good way to get past the coastal mountain range, then you are in relatively flat land all the way to Spokane.
Storms in the PNW (the notorious pineapple express) have a habit of hitting about every two weeks in winter. Follow weather forecasts and watch out for wind especially on high plateaux once in-land. Better to stay parked than to fight a side wind.