Continuing about the stray/homeless cat I feed.

I live in Midwest and we will have temperatures down to 20's and wind
chills into single digits. I don't know what she did last winter.
Actually I don't know if she would even need my help this winter. But I
want to have some help for her on my porch should it be needed.

I would be most grateful to hear ideas from those of you who have
created warm corners to ferals.

I have been reading around and lurked in the ng's as well and this is
what I have so far:

Two styrofoam coolers, one inside other, a hole cut out for entry/exit,
a layer of blankets with the microwavable heating "frisbee" (forget the
name) under them. Do I need extra insulation between the walls? I can
even cover the entrance with hanging strips of plastic the way they
have in some grocery store freezers.

I have no building skills but this I can manage. It would also be
affordable enough and if she doesn't use it, well, I'll have no
regrets.

I have outlets available but am afraid of using electrical devices, of
causing a horrible harm with good intentions. However, if you have
experience with something that is absolutely catproof (in your
experience, not manufacturer's claim), I can consider it.

All comments and suggestions appreciated.