I would check with Flying Flags in Buelton to try to get near SB. It's a fantastic park with good climate and things to see and do in Solvang, Cachuma, and Santa Ynez.
To get close to LA, I would call Valencia Travel Village. It's a good location with LA 45 minutes away if you avoid commute times and Ventura beaches less than an hour away.
Ventura also has a nice RV park that's equidistant between LA and SB, but they're crazy expensive and probably booked. Ojai also has some good spots. I think their KOA reopened after the fire.
I've never stayed at the RV park right off the 101 in downtown SB, but I assume they're already booked. Same with the one in Goleta.