I should add that keeping the heater on all the time comes with some
caveats. One being the whole engine has to get hot and in most
climates where it's necessary to preheat the engine that means
thoroughly wrapping up the front of the airplane from the firewall
forward. The blankets I've cut go half way up the windshield and
behind the cowl flaps.

The problem with keeping an engine too warm all the time:
degraded rubber hoses, seals and gaskets. Rubber parts lose their
lighter elements faster when hot and get hard; they shrink, crack and
leak. They'll do it over time too, of course, but heat accelerates it.
The same thing applies to aircraft interiors and radios when subjected
to the heat of the sun.
Nothing lasts forever. We don't want to think about that
sometimes. Your airplane is aging whether it's flying or not, and you
can only slow it as much as practicable. I would be more inclined to
use dessicant plugs (with "Remove Before Flight" flags attached) on the
engine breather, exhaust and intake. Cheaper than heating and easier on
rubber.

Dan