Ron,
We recently spent two weeks in Napa/Sonoma and stayed at the fairgrounds in Sonoma. While our preference in the area has always been the Napa fairgrounds, it is often difficult to get reservations. That was our problem this year so we gave the fairgrounds in Sonoma a try and were pleasantly surprised. Not spectacular but adequate, very reasonable and in a convenient location. The sites are all gravel, level and have full hookups. They do have limited 50 amp sites but are usually only in short supply during fair events.
Tim