Detouring from the coast to Crate Lake is, roughly, a 2 day affair - east on US199 and US62, overnight around the Lake, back on OR138 and OR42.
An alternative to going up the Washington coast, would be go through the Columbia Gorge once you get to northern Oregon.
Then go north of US97 to Yakima, and US12 or WA410 to Mt Rainier. Or take Wind River Rd north (paved forest service) north to FS99, and FS25 north to Randal on US12. On the way, take the side road to the east side of Mt St Helens (maybe leaving the trailer near the turn off).
The east side of Mt St Helens doesn't have the visitor centers that the west side does, but the views are just as good. Check the Monument website. Also the relevant forest service district.
Having seen St Helens and Rainier you could go NW to Olympia, and take US101 north to the Port Angeles to the see the N and W sides of Olympics.
Then WA20 and ferry to Whidbey Island (check the state parks) and on over the North Cascades.
You could continue of WA20 to Idaho (US2) and Glacier Nat Park, or cross to southern Washington and US12 to Lewiston. Possible central WA sites are Grand Coolee, Banks Lake and Dry Falls. And COE campgrounds along the Snake River.
Check the Hells Canyon website for suggestions on how to view that Canyon. Many overviews and river access points involve rough gravel roads.
US12 will take you over Lolo pass to Montana.