Dave wrote:
It seems to me that a low-voltage pad heater would fill the bill. The
following link is for a company that makes pad heaters much like the
Tanis, but designed to operate on 12 Volts:

Are you suggesting installing the 12 V heater along with the Tanis
heater, or instead of the Tanis heater? If the 12 V heater replaces
the Tanis heater, you then need to carry a 120 V to 12 V transformer
or power supply if you want to preheat your engine at a remote location.
Assuming you have a 250 W heater, browsing Digi-Key says that a 250 W
transformer weighs about 6 lb and costs about US$75, while a 250 W
power supply weighs about 3 lb and costs about US$250.

Matt Roberds