Howland Hill Rd is relatively short, with trees closely lining both sides. You'd be lucky to find a place to pull off to take pictures, much less boondock. Plus it enters park (state or national) almost right away.
When I toured the area a decade ago, I drove up 199 to Patrick Creek, camped over night (small forest service campground), and then returned to the coast on forest service roads high on the ridge to the north. Old wagon roads tended to follow ridgelines, rather than the river bottoms that modern highways favor.
In Prairie Creek State park, I recommend driving to the shore at Gold Bluffs. There's a nice campground among the dunes, and an easy hike in Fern Canyon (almost like the Olympics). Lots of elk as well (to watch and be watched).
I haven't driven it, but on the map (and photos) Bald Hills Rd looks interesting. It crosses the mountains, eventually meeting CA169. 169 follows the Klamath River north, but does not reach the coast. South it connects with 96 and 299 back to the coast.
Bald Hills is also the the access road to Lady Bird Johnson Grove (I think), which may be an easy enough walk through big trees.
