ACA Sierra Cascades route - will campsites still be open in Sept -Oct?

[mcmoonter]

I'm still pondering my trip for this autumn. I'm thinking along the lines of riding down the Pacific Coast possibly from either Portland or Sedro Wolley to San Francisco, then catching the train up to Klamath Falls,OR to return North on the ACA's Sierra Cascades route.
I've been caught out in Oregon after Labour day when a NFS campsite was closed down for winter. Will this be typical along the SC route through OR and into WA? If so what other camping alternatives will be out there?