Going through Astoria isn't too bad. Just take highway 30 over to Longview. Head through Longview to I-5. Then head North until exit 95. Go East until the road hits a T, turn left and the park will be on your left.
Finding the part of the camp that we use is much harder. Follow directions to the boat launch, Most of the way to the boat launch (there's a large circular parking area), you will find a road to the right with a sign that hopefully says Alliance Seattle (sometimes it doesn't). Follow that long road until the end and you should be at the "tavern".
Hope that helps.