The problem isn't freezing, it's the hard freeze that will damage pipes. I think you're okay at 27°F. The water in the freezer analogy doesn't work since freezers are normally set at 0°F.
If your 27°F forecast isn't accurate for that location then you could have a problem. I've seen variations of 10° in weather stations around here. The forecast you see is probably at the airport. It could be colder where you're storing your motorhome.
Weather Underground has a map that switches from radar to cloud cover (satellite) to weather stations. You might check it out to get a feel for how temperatures are running near the storage lot. Look at their "Wundermap".