... I did put 2" rigid board along the exterior wall outside the pipes so they do have some insulation. After this latest episode I also installed small grates to allow house air to get into the pipe space. My hunch is that should help alot (it also enables easy access to the pipes).

Normally when we get severe cold spells I open the curtain that blocks the upstairs off. I forgot to do so this time, and I don't want to rely on that especially as we'll have renters/housitters next winter.

I think installing the unit in the bath, which is tiny, might be the answer, and hopefully it won't be too costly to keep the room at 45.