According to Dutchmen the RV's aren't supposed to be used in temperatures below 30°
I guess their definition of Arctic varies from ours.
You will need to try and insulate that specific pipe if you can, otherwise as pointed out, leaving it drip is your best bet, also don't forget to leave the gray valve open.
Outside of a very few brands like Northwood Arctic Fox
or the Bigfoot
, most RV's are not really designed for 4 season use. More like 3 or 3.5, that doesn't mean you can't do it. Just that you will have to adapt.