You can vape in every other county in the state...as long as the establishment allows it. I vape in bars in Snohomish county all the time. In king county, it is illegal, but in my experience most people dont know that, and most people dont care. There are several places that i frequently vape in within King county, and the employees are cool with it. If you are going to be near tacoma, stop by the vaporium and say hi. They have a lot of flavors you can sample, and they are really nice folks.
I don't go on hour + long shopping trips, but if i were at a mall for that long, i could easily vape without bringing attention to it. I dont usually vape in stores, but i do in coffee shops, some restaraunts, and most all bars i go to. The trick is to not make a big deal out of it. Don't blow huge clouds of vapor, and be tactful about it.