The piping is, for the most part hose, not pipe. It's the bib/mixing valve fixtures that would have to endure the stress. In some cases that's metal (like the forward wash down; however, the cockpit showers are usualy plastic).

Anyway, if you can, I'd see if you can get something done. if you have a water maker, that's in an exposed area, I'd run antifreeze through the internal plumbing. If you can get a heater in there, then I think you'd probably be okay (unless it was already damaged).

Jon, if I were near by, I'd run out there for you, but I'm 4 hours away by car.