laptop heater

I need to keep a labtop in a unheated shed. The labtop spec says that
it should not be used below 55 deg F. I would like to make a box with
a heater to control the temperature. The shed is enclosed so that I
have no problem with moisture(rain or snow).

Two problems. I have attempted to find thermostat switches between 60
and 80 deg F with no luck. Do they just not make them? Also I am
being buried in information about heaters. Can someone provide a
recommendation about a flat heater(1 or 2 inches thick) that I can use?
Preferably surplus.

Thanks
george

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