Well, this was a bit different.
We have had cold nights (down to 8 degrees) before this season with no issues. My water line has heat tape run along it's length encased in foam pipe insulation. Dump bay (drivers side) is heated by furnace. Holding tank area is heated by ambient heat from flexible furnace duct.
Water heater above dump bay (drivers side), back side under the bathroom sink cabinet (inside). Toilet in on the same side of rv. Shower and kitchen are on the passenger side. Water lines to run across rv in tank bay for the shower and kitchen.
Had a cold night Friday, down to 12 degrees. Got up Saturday morning and had a strange water issue:
Hot/cold water worked at the bathroom sink and toilet.
Hot water at shower and kitchen.
NO cold water at the shower and kitchen.
Opened the cold water at the shower and after about 10 minutes it started running. Back to cold water everywhere again.
Strange that the cold water pipe "froze" inside the enclosed, insulated bay.
I plan to look at the pipe runs and location of the heat duct to the pipes. Will move duct close to the piping to help keep them warm. Could add a vent in the run (flexible) IN the bay to add heat, too.