Been a while since I've been here. Blowing out my water lines today and came back by to see if I'd forgotten anything since last year, and this old thread popped up in my search.
I wanted to let everyone know my experience with just draining my 2018 Hawk side dinette several winters ago, and why you shouldn't just worry about your water heater tank. It was our first winter in a real cold environment and I forgot about blowing the lines out. I drained everything and thought I was good. The next time I filled the tank and turned on the pump (had not hooked up to city water, but results would have been the same), water started pouring out of the front-most cabinet. Not a lot of water leaked into the camper because I turned the pump off immediately but I knew there was a problem.
I located the leak by shining my light into the cabinet and turning the pump on for a second. There at the very top of the front cabinet (behind the upper drawer), mounted just underneath the countertop, was an ABS manifold that clearly had a crack. This is the cabinet on the 2018 Hawk that houses the waterheater, pump, and fill line down to the fresh tank. I removed it and identified some manufacturing numbers on it, and emailed FWC about a replacement. They wanted a lot for it, so I decided I would try and find it myself; ID'd it as a globally manufactured 5-port pex manifold, and found it on Amazon for 1/4 what FWC wanted. It was an easy replacement, but the point of the story is that there was enough water in the low spots in this manifold (at just about the absolute top of the water system; not a low spot) after draining to crack the cheap ABS. In winters since, I have blown out the lines and not had any trouble.
So, if you are wintering your camper anywhere that actually has a winter, I would not skip blowing out the lines. Your drained WH tank should have no issues, but these little cheap fittings can take much expansion.
