I live real close to that. Little bit off topic as you said you wanted a campground close, but if you need to park when hooked up Randy's Restaurant in the back lot at 47.513016,-122.293293 has room and not uncommon to see rigs parked there. Restaurant is real "greasy spoon" but also has a lot of old Boeing stuff in it. Museum is short walk away. Just in case you wanted the option of camping somewhere else or out a bit more but also want to see museum as your going by. You could also park closer but more of a hassle IMO