I had a hard time finding a RV park close to or in Napa through Google or or other means.
The Skyline Wilderness Park is only about a mile from downtown yet you are at the foot of the nicest 22 mile of view trails anywhere. The park can take tents and 40' motor homes and yet feels very private with no noise. We took a short 1 hour hike and came across (4) different deer, one of which actually continued walking toward us until it decided to walk off the trail.
We showed up at around midnight and they let us stay in a parking area until the next day when our spot actually opened up at no charge. The people that run this park are very nice and we will be coming back!