My daughter and I took six out of the eleven days of our 2016 summer overland trip to do the entire route of the WBDR in 2016 (south to north) with our Sportsmobile.
Day 1: The section from the Columbia River (WA/OR border) up through Packwood did have a few short sections where the tips of the fir trees rubbed down both sides of the van. One section of the road had half washed out but we were able to tippy-toe around it and keep moving.
Day 2: The section from Packwood to Ellensburg: This section had one short route that was too tight for us (NF-324/NF-325). We were just too tall. We were able to get around this section by using NF-1500. We occasionally had great views of the various volcanoes.
Day 3: Ellensburg to Leavenworth: Lots of elevation gain. My favorite part of the trip. Lots of cliff driving. We did it when it was dry. One section crossing a rock slide was very questionable. Had to stop and move lots of rocks around to reconstruct/stabilize trail. There were no re-routes to this section (other than to back out and take the highway).
Day 4: Leavenworth to Chelan: Lots of overgrown patches with branches dragging down the side of the van. Fir trees had been dragging down the van on the initial stage. Now, there were stiff desert shrubs doing the same thing. I seem to recall that the 'jungle' section was on this day (lots of brush over the road). We opted for the other WBDR alternative that skips this. We had one short re-route because the road we were supposed to be on got washed out by a previous storm and it was not fixed yet.
Day 5: Chelan to Osoyoos Lake (Canadian Border): Deviation from WBDR route. We did the first half of this route then we opted to drive up the highway to Lake Osoyoos. We would then return on the last WBDR (north to south) the next day to complete the route. This was the dustiest day of the trip.
Day 6: Osoyoos to Twisp: No narrow brush sections to deal with today. Just cows. Lots and lots of cows.
Awesome trip overall. The van was large enough that we had to cut blow-down away every day. We did not see any other automobiles doing this same trip but we did encounter a half dozen adventure motorcycles. The route is rough in places, dusty, and the vegetation definitely encroaches on the route. We only had to use 4x4 during the one really technical rock slide section on Day 3. We also had to pay very close attention to the many fires that occur in the area. It should also be noted that for as much vegetation that dragged down the side of our van... after a wash and a detail, no significant scratches were visible (paint still looks like new).
If you want an alternative that goes many of the same places - and on a slightly more open forest service road track, see the following: