Caring for a stray (2): Winter preparation

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.

>All comments and suggestions appreciated.

What they mostly need is a place to get out of the wind. Animals will
curl up and generate their own heat. They're wearing fur coats, after
all. You can set up such a place and put an old blanket in it
for softness if you like, but there's no need for electric heating
anything, really. Unless it gets really bitter cold (like in the
minus double-digits), they'll be fine.

Jane