Don't forget that there are 1/2" drain tubes hanging below the bottom of most RVs; those can freeze and break. The other thing to consider: on a calm night, it could be 28 degrees at the weather station; but if you are down in a "bowl" the temp could be 5 degrees colder.
We had a 3-way valve installed on our pump that drew AF through the lines. We could winterize several times over the course of a couple-week's winter vacation - it was no big deal. The important thing was to haul AF along with us, since it was harder to find down south....LOL!