Is it worth lugging long extension cords to plug in the Tanis heaters for my
Baron if it's going to sit outside at 12 degrees for two to three hours
after a flight?

I have cowl plugs which may help a little, but is it really a problem? The
oil will be well circulated, and the battery is in good shape to crank the
engines.

Also, the POH says to keep the cowl flaps open during taxi and take off, but
when it's so cold outside does this still make sense? As long as the CHTs
remain within a reasonable range what difference should it make?

Thanks from Wisconsin, where its 2 degrees and clear.