Great selection of fuel stops at the corner of I-5 and the 12. FlyingJ, a really nice 76 with access I prefer, and a few other. From there you will have no trouble getting North of San Fran with access to big rig fuel stops. Taking the rig through Wine Country Napa is a bit problematic as most wineries do not have RV parking and access to many is along long narrow roads. I'd suggest basecamping in Vacaville and taking the car on a day trip though Napa. We've stayed at Vineyard RV in Vacaville a few times (friends live in the area) and would recommend it as a base.
Happy Trails.