The last, and unfortunately only, time we made the Olympic Park loop, in 1996, we spent a couple days in either a State Park or Natl. Park campground where the Worlds largest spruce tree was; Keith and Bill probably know which park I'm referring to. We did a little fly fishing on the lake that is there and did some hiking.
At Port Angeles we put in at a private RV park that's been there awhile, put the German Shepherd in a veterinarian's kennel nearby, and took the ferry to Victoria for 2 days, staying at the motel across from the ferry docks. If you elect to stay overnight like that, make reservations first and don't forget your Passports these days.
It's been since well before then that we crossed the North Cascades, sleeping one night in the back of our '82 Toyota SR5 pickup. I recall a pretty decent road and would expect it to be at least as good now. It does wind around and through the mountains, but the views are great with pull outs that allow time to fully appreciate them. Similar to Glacier Park's Going To The Sun Highway in scenery, you can do so from your coach in North Cascades; GTTSun road is no place for a motorhome, so you will have to spend a day on it in your toad after parking the coach in a campground at the east end. Then take the road westbound that's south of the Park.
You may consider a sashay south while taking Bill's Idaho Panhandle route, so to see not only Sandpoint, but also Couer d'Alene, and the lakes of the area. We've more often traveled the Missoula/Kellogg/Cataldo Mission path because of the facilities and mining histories and tours, museums, and mountain trams, etc. along the way, and the Mission. There was a relatively undeveloped campground near the mission at the west end of the route from which we took the toad south and west on explorations.
I have fond once-in-a-lifetime memories of largemouth bass fishing one evening at Round Lake, maybe 10 miles? south of Sandpoint. We stayed at the campground at the lake, but the Pace Arrow made it through its tree-bound road where I'm not sure a Beaver would - check ahead if you go in case things haven't improved. But dang if I haven't dreamed of returning for another experience like one bass per cast and the one that hauled my boat across the lake, then wrapped his hog-like self around a deep log, never to be seen!
Joel
PM or email me for the secret of fishing Round Lake if you go