Warning. On my 2011 Eagle 365 BHS the dealer ran water through the WD hook up to make sure it worked on PDI. I wanted to kick his hind side for this.
The first time I winterized the unit I ran antifreeze through the WD lines then valved them off from the factory installed valves in the ceiling of the basement storage. Never looked back. I do think the line held antifreeze before the valves.
I plan to winterize my NorthPoint 377 next weekend. On the list is to see if there are any valves installed. I have not found any valves where the eye can see. If valves don't exist i plan to install them at lowest possible point. I will winterize though the lines Close the valves and never worry about it again. I also plan on removing the whole house filter as my friend gets really stinky water if it sits in storage for a period of time. I have a whole house filter that I used on my 365 that has garden hose connections on it that I plan to use.
I hope this helps.
Derek, Wife, and 3 kids
2016 NorthPoint 377RLBH
2015 GMC Sierra 3500 DRW SLE Duramax
B & W Companion