Best Bike Camping Tour Out of PDX?

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I am looking for a safe and scenic overnight bike camping trip to do this October.

The trip requirements:

-Need to be able to camp somewhere cool and not annoying
-30-50 miles one way
-mainly on pavement
-mainly flat but some hills fine
-wide shoulders or rural roads
-Can do in a weekend.
-Taking Max to get started OK.
-Please provide route!

We are beginners, and loved the Banks-Vernonia trail, but want to do something different this time.

I will be going with one other person and we both have entry-level touring bikes (Trek and Surly)