My experience with a 30-foot C is that the narrow, winding steep roads are not what is treacherous. I've driven quite a few in Colorado, Utah, New Mexico, Arizona. I find most of this mountain driving to be at rather low speeds, with speed well controlled by engine braking.
The really treacherous roads for a RV are crowded urban freeways with aggressive drivers trying to get around and ahead of you: passing on right, not yielding on merge, cutting across in front to brake hard for their last second exit. I'll route way around to avoid that traffic, but those are going to be really hard to avoid in Southern California.