I hear stories of people who say they've got tickets, however, I have lived in California all my life, have towed either a boat, a utility trailer, or a car behind the motorhome for the last 35 or so years, and was a cop for 28 years. I have routinely fractured the 55 mph limit when towing and have never been pulled over for doing it. In fact, for all my years of driving my RV and my dad's RV before that, I've only been pulled over one time and that was when somebody stole my electric adapter from the trailer I carried my motorcycle on so I couldn't plug in the tail lights for the trip home. In my time as a cop I never enforced that law either, but then again I was a City cop so there wasn't really places to enforce that section as the fastest speed limit on any road in town was 55 anyway.
So if it is heavily enforced, I sure have lucked out over the many years. But also, I don't make unsafe lane changes, and don't follow other vehicles too closely. CHP tends to notice your speed more when combined with things like that.