Humboldt Redwoods SP may be our favorite area for viewing redwoods. A little off the beaten path so quieter. We've stayed at Burlington CG right next to the visitors center, but be warned, if your rig is big, the interior roads are tight, although we've seen 35'+ RV's in there.
Jedediah Smith Redwoods SP is often mentioned as a good camp spot, but we once drove through when it had been dry, and the dust was unbelievable.
Around Redwoods NP are several CA SP's with CG's. Gold Bluff's Beach is right on the ocean, but no hookups and no reservations. Once the fog rolls in (from what I understand, a little later than your visit), it's sometimes nicer to stay inland a little. We've used Panther Flat NFS CG up US 199. No hookups, but coin operated showers available. The last time we visited the redwoods in northern CA, we stayed at Harris Beach SP in OR and commuted down. OR SP's are just spectacular and usually less money for more amenities. (Sorry Californians :) )