If you can get a reservation, Rasar state CG is spectacular and only a few miles west of Concrete on HWY 20. If not there then Sportsmans CG looks OK but we're never stayed there.
There's also a nicely kept Thousand Trails/KOA in the same vicinity of Rasar that looks pretty nice and has great amenities for kids.
If you want to be further away between Issaquah and Everett then about the best place in the area is Lake Pleasant RV resort in Bothell Wa. It's a very nice quiet park in close proximity to stores and restaurants. (I live close by)
