My last house was plumbed entirely in PEX and it was great. We even lost power once for a week in the middle of January and half the lines in the house froze up. Zero damage when they all thawed out again and no leaks.
We rented a mobile home one time, furnace ran continous in the dead of winter. Water lines ran the length on the inside walls.
They froze. Broken plastic everywhere. When i discovered it, i turned off the water, turned heat down, removed cylindrical ice cubes and replaced the plastic.
Brought heat back up and went under mobile to figure out why.
The ducts were cut open every 10 feet, and crawlspace was uninsulated. Wasnt very long before i got tge hell outta there.
I know pex is freeze proof, i will make do with the temporary setup until spring. 45 gallon drum should do ok with the low flush toilet.