I live in the Bay Area and drive to So Cal on a regular basis. There are only two routes that you really want to consider in my opinion assuming you want to get to DL as fast as possible. Both are almost equal times and distances.
First is HWY 80>580>5 south. This is the most direct shot...especially for a RV, but depending on when you leave can be a bad choice. If you are headed that way in the 3p-7p time frame, forget about it. 580 though Livermore Valley in rush hour(s) will make you WISH you were in LA traffic. I lived out there for a few years and it is still rated as one of the worst commutes. If you are leaving in the AM or night...go that way.
Second option is 280>85>101 down to Gilroy then across 152 to 5 South. This is the "go to " route for everyone on the South Bay to LA. If you are in rush hour, you will hit traffic getting through San Jose, but not nearly as bad as 580.
If you are not anywhere around traffic times, you can take 101 south through the peninsula, but I always go 280 headed down to Gilroy where I am originally from.
101 all the way south is an option but tack on at least an hour or two.