While the traffic around Seattle is no fun I suggest that it is overrated. We have been in the area a few times with the 5er. We apply the same MO to Seattle as any other city. Avoid transiting through during rush hours.
At any given time Seattle has nothing on the Washington DC Beltway at any time, Atlanta, anywhere near NY, Boston, Baltimore, Philadelphia or Hartford. Done them all. I'll take Seattle over all of them & some more.
For camping in the area we have used Saltwater State Park not far south of SeaTac. Tight interior roads & not many big rig sites but very doable.
