Elks organization? No..
Will it still be that busy in early Sept during the week? I will look into the reservation system and see what I can find.
The demand lightens up in the winter months because kids are back in school. But not all the parks are open year round. If you get north as far as Seaside, check out Circle Creek RV park. Great park, will handle your rig and friendly owner. It is also a good home base from which to plan many different day trips. 30 min. to Astoria, 15 min. to Cannon Beach and 2 hrs. to Portland.