If doing this one should be able to tap a line just before and after the water pump. By doing this you could circulate the heat in the block the way it does when the car is running. The lines would be connected to a heat storage tank when sitting for a night and slowly circulate the coolant to attempt to hold it close to a preselected temp. The tank I figure would be set up like the home built storage tank here
http://ecorenovator.org/forum/conser...cumulator.html with a small pump between.
If the run for the lines is a little long then find a tube larger than the line that you are running and use it as a sleeve to reduce the direct transfers of heat sealing the ends with foam.