Travelling and camping along the west coast during the summer pretty much requires reservations. The coastal state parks in Oregon are very popular and booking well in advance is a must. Parks along the southern Washington coast are also popular spots in the summer.
If you have access to a directory of RV campgrounds and resorts, such as Woodalls, or something similar and have your route roughed out, going through these resources will give you an idea of what is available other than Good Sam and KOA campgrounds.
Another good source of parks with reviews can be found online here:
www.campgroundreviews.com