Here is some info for you to digest
Steel Park
The nicest place to stay with your RV , space is limited and crowds are small. However you will be staying in a gravel parking lot with no hook ups other than water. The lake is right behind you and your boats can float right behind your RV. Pumpouts are in the same lot so that isn't that big of a deal. Restaurant(sp)and store are nice and well stocked.
Rancho Monticelo
Nice RV spots covered by trees and sort of secluded, you will still have neighbors but it is not that bad. The resort is usally pretty quite but it doesn't have much to offer other than a snack bar. RV spots are no where near the water. I believe that they have full hook ups there, buy I dont remeber.
Berressa Marina
All RVs are out on a parking lot type point. The marina will launch your boats as soon as you arrive and take your trailers to another lot so you dont have to deal with them while you are there at all. They have docks right below the RVs for all of the boats. By far the best veiw of the lake from your spot. They dont have full hook ups but they do have water and they have a guy come pump your RV where it sits at no charge. Very few campsites so there really is no problems at all. They have a great store and restaurant and a really nice resort.
I know others will have their favorites but I would do Berryessa Marina if i was staying for any length of time. I have been going there for years and will continue to do so as long as I can.
I hope this helps