I will answer your open carry question. It is not illegal to openly carry a rifle in Washington, HOWEVER, and this is IMPORTANT - maintain muzzle discipline! The minute that muzzle sweeps someone, you can now be charged with 9.41.270. It would be best, if not in a case,to carry slung over a shoulder with the muzzle straight down.
The rifle can even be carried loaded, but not loaded in a vehicle.
Your best bet would be a cheap rifle case.