There is a great RV Resort off I-5 between Portland, Oregon and Seattle, Washington. It’s called Toutle River RV Resort. I discovered it on my travels across USA on my Harley.
They have a nice area for bikers with the laundry and restrooms very close by. Being a female traveling alone I felt safe at this campground. I had a spacious site under big fir trees with a community fire pit, volleyball and horseshoe pits nearby. It was great to stretch my legs on the river trail.