When you are camping/living in an RV and the temp drops below 32, like 27, the water lines inside the RV usually won't freeze at all. The outside hose probably will especially at the wall connection.
That said, your water lines have a good chance to freeze if it is just sitting there unoccupied. In your case, just blow out the lines with a portable compressor. Dump the water tank and don't put that much into it when you do go RVing. Probably you won't need any at all if your stay are RV parks.
We don't put water in our lines until we get to southern Ark or Okla. We carry water bottles until then. Works just as good.