You may open carry unloaded in the vehicle, or loaded with a CPL. RCW 9.41 Is the WA code on firearms and dangerous weapons. Easy read. Not cluttered at all.
You may open carry loaded everywhere as long as you are not in a vehicle, except those places listed in 9.41 Local goverments cannot go beyond state law. (you know, court rooms, jails, that kind of stuff. You can carry in parks etc.)
There is only one funny restriction...rock concerts, the rest make pretty good sense for these days.