heres a lesser known site ..
20mile bay is nice
http://westharrisonreservations.com
theres also chehalis lake.. they used to have adds on craisgslist to reserve
IMO.. theres no point going to camp sites at 7am.. if the sites full and if people plan to leave that day they wont leave till check out.. which is 11am
best to go around 10.. scope out spots.. see if people are leaving.. then talk to them
also check government campsite hourly as people cancel all the time.