We were in the area last month. The problem we found is that it isn't the sites that will limit you, it is the roads and the trees. We found a few sites in which we would fit comfortably but would be difficult to get to. And they were all taken anyway. Between the low clearances, un-level sites, and awkward entry angles, two or three days wasn't worth the hassle and potential damage.
Not sure if this will help but it is an option. At Benbow, a few short miles south of the Avenue of the Giants, there is a nice KOA. Easy in and out.