I know too well from experience. And the soft copper I have runs from 3 tanks. It was put in as the boat was built and will last forever, if it doesn't freeze. I don't have much choice except for potable anti freeze. The stuff is nasty but we have never used the tank water for drinking in any of our boats(even this one with monel tanks and copper supply lines).

Hose or Pex can freeze with only potential leaks at fittings, if at all, if you miss a plug of water. Your idea is great just to eliminate one more nasty substance we use.