I too have been trying to solve the problem of vacant cabin + freezing temps + off grid. I have a 55 gallon drum indoors that is my source of water that I plumbed into to the bath and kitchen sink.
My recent improvements:
1.Moved the water line inside (no longer does it travel beneath the house). If frozen it will thaw once cabin is warmed up
2. Using PEX piping since it will not rupture from a freeze
3. I have a drain line; when I leave I close the main valve and open the drain to purge the line
Next I'll incorporate a copper pipe that can pass water by the wood stove so I don't freeze my hands washing dishes with 42 degree water!
So far I haven't had the drum freeze solid, water changes temperature very slowly more volume takes more time (high latency of heat) I visit once a week and get the place up to 70 degrees and that seems to be working. If you have electricity you can wrap your pipes with that heating element they sell at Home Depot etc. My solar battery bank just doesn't have enough juice in the winter to keep up.
I hope that feedback helps someone!
