Drive west over Skyline on CA-84 and sleep under old-growth coast redwoods at Memorial Park in Loma Mar, the peninsula's own redwood campground and the closest one to Mountain View where a van fits. The Sequoia Trail passes the largest redwood in the park in under a mile, and the Tan Oak loop threads fern and redwood sorrel down toward Pescadero Creek. Sites have no hookups and RVs top out at 35 feet, so plan on a self-contained night rather than a full-service pad.
Azalea Flat books year-round while Sequoia Flat and the dump station open only from Memorial Day weekend through October 31, so a winter overnight means Azalea. Either way the draw is the walking, not the pad: Sequoia, Tan Oak, and the Creek Trail along Pescadero Creek.
Portola Redwoods, deeper down the canyon
Portola is the one park people actually search for out here, and it earns it. The road drops off the ridge into a shaded canyon of redwoods, past Peter's Creek Grove and waterfalls on Fall and Pescadero creeks. The catch is size: motorhomes cap at 24 feet and trailers at 21, and the way in on Alpine Road is steep, winding, and out of cell range. Unless your van is small and Portola is already your booked night, sleep at Memorial and drive in for the day.
Half Moon Bay and the San Mateo coast
For the salt-air overnight, Half Moon Bay and the rest of the San Mateo coast are covered on the San Francisco campervan page.
Henry Coe and the Santa Cruz mountains
For Henry Coe's backcountry ridges or the redwood parks around Santa Cruz, you start closer from San Jose, and those overnights live on the San Jose campervan page.
Bigger rigs and the long road trips
A campervan clears both length caps with room to spare; if you'd rather size up to a full RV, the California RV page has the bigger rigs, just mind the 35-foot limit at Memorial and 24 at Portola. The marquee road trips out of the Bay, Yosemite, Big Sur, the wine country, and Tahoe, each have their own page off the California campervan hub.