When are you going? It makes a difference because of the passes that are closed. If it is in the summer, and you go over 20, I would stop in Winthrop or Twisp. Pearrygin Lake State Park is near Twisp. Leavenworth and Chelan area also great stops. I also really like Bridgeport State Park on the Columbia near Brewster WA. You can filter to find parks with the camping facilities you need and see places to stop at https://maps.northwestportal.com/outdoors