The Delta is an agricultural area east of San Francisco and south/west of Sacramento. There are many lovely parks all along the many rivers and inlets which make up the Delta region. San Francisco is a good hour away by care, at least, with traffic I would almost plan on a 2 hour drive to the tourist areas. Because there really are no straight shot roads to Sacramento it too is about an hours drive. For an extended stay it is a lovely area, but remember, winters can be wet (by California standards) in that region, and an El Nino is predicted for this winter. If you are just planning to vacation and visit the Bay area there are many closer regions that would make the visit more convenient. Petaluma KOA or Pasifica RV are both lovely parks. Near Napa we like Vineyard RV in Vacaville.
Happy Trails.