Don't know what type of rig you have but Odlin Park on Lopez Island is a wonderful campground-dry camping no electric..and Moran State Park on Orcas Island.
I did a write up on Lopez here:http://roadtrekgirl.blogspot.com/2012/09/odlin-park-san-juan-islands.html . She spends a great deal of time in the Islands and they have a 26ft Airstream. Have fun, it's a beautiful place to stay.