Hiway 166 Bakersfields to Santa Marie?

If you are not in a hurry, it isn't a bad route. Mostly a two-lane road with some sections of moderate curves. Lots of trucks use this route. A bit of climbing after leaving Maricopa. The most curvy sections are between New Cuyama and US-101. We drove the route both ways many times in a 27 ft Class C towing a Jeep Wrangler. We haven't yet driven it with our 39' DP towing a Jeep GC, but wouldn't have a concern. The biggest concern are other drivers in too much of a hurry. The next alternative I'd recommend is north on I5->CA46->US101 at Paso Robles and then south to Santa Maria. But that is quite a bit further. I wouldn't recommend CA58 in that size rig as it is very curvy.