"How about one of those katz,inline lower radiator hose heaters? "

I used one of these in may nissan sentra some years back when the temp would barely get above 0 F and -25 below was common at night (Central Maine). It worked great - plug it in every night. But I have to say that after 7 or so years - the sentra with the heater had head gasket problems, and my other without the heater never did.

I've used the magnetic plug in block heaters on the oil pan for my cub tractor and air compressor. They work but not so well -- always plugged in.

A strong battery makes all the difference.