I would definitely advise avoiding any of the 'long term' spots at the north end of santa cruz. Those have become pretty transient and sketchy. Well north of santa cruz, say 5+ miles and you can find lots of turnouts, however. Van friendly with great views. I'd recommend staying north of Davenport. Turnouts are right next to the highway so they'll be pretty loud. Some turnouts are bigger than others.
North of Davenport near Pigeon Point lighthouse is a road that closely parallel's the highway just north of the lighthouse and essentially dead ends into the driveway of the lighthouse as you head south. If you head there you'll find it. The driveway of the lighthouse takes you back out to the hwy. It's a good spot to stay overnight and hides the vehicles from the highway well. Sidenote: Some large parties may or *may not* have been thrown there over the years.
It provides excellent beach access with the lighthouse on the tip of pigeon point just a few hundred yards to your immediate south. It's an active lighthouse so if you don't have solid curtains that will be a problem.
Costanoa KOA and seeing those grounds is also worthwhile and accepts vans. Ano nuevo elephant seal colony is right there. That's worth a visit. In general, there's great coastal hiking and beach exploring all around the lighthouse down to ano nuevo and beyond down to waddell creek. Highly recommended.
Another close option is the dirt road just south of the Costanoa entrance on your left as your heading south. It's across from the lighthouse a bit south and on the mountain side of the highway. It takes you up to the chalk mountain trailhead a few miles up. THat's a great hike if you're into it. Provides some incredible views. Otherwise the road just up from the hwy on the way to the trailhead is a good spot to stash camp. It'll get you away from the highway where it's a bit quieter.
It's my home turf so fun to share! The stretch between San Francisco and Santa Cruz is a great section of the California coast. Each of the California sections are all quite unique. Wherever you land, enjoy!