There are at least a hundred park and fly lots near SEA and the cruise industry has several very large lots at the pier. I saw RV's in both areas this summer, but do not know about hookups. The "cruise" lots are expensive, even for a car, so you could probably do better finding an RV Park and paying the weekly rate. The private park & fly lots near SEA are less than ½ the cost to park a car as the cruise ship lots and there are many transportation companies to get you to the pier.