Easy deal on the Cowlitz...get a map and look for the Blue Creek Hatchery that's up river and east of I-5. There is a huge WDFW parking lot/boat launch there that allows overnight parking and I have seen people have camp fires there (although sometimes it's posted no-fires due to fire conditions, so be sure and check with the hatchery people there if it's ok). You have to have the red/white WDFW parking sticker that comes with your license displayed on your rear window to park there. It's free other than that. You can fish just down river of the parking lot by walking down a meandering quarter mile+ trail to where Blue Creek comes in to the Cowlitz...combat fishing stress relieving care package may be required however.

Good luck!