Not Santa Cruz but just South of Castroville off Del Monte blvd I saw about a dozen RVs boondocking. I highly recommend going to Felton and riding the steam train (Roaring Camp Railroad) into the redwoods.There is also a diesel train to the boardwalk in Santa Cruz. On Wednesdays they have a deal that everyone is kids price. Park in the Henry Cowell State Park and walk across to train $10.Same price that it costs to park at the railroad parking but closer and gives access to the beautiful grove. Easy trail through the grove. We spent the whole day there til closing. Don't miss the Bigfoot Discovery museum just across from the State Park.
