You could leave the heat on at 35 degrees, which would mean a special thermostat. If you shut down completely, make sure to eliminata ALL sources of water! Do you have a frig with automatic icemaker? Also, unplug the frig, the compressor oil will get too thick. Do you have a washing machine? I like the idea of providing enough heat to keep thinks like wood and cement from shrinking too much. If you do leave the heat set low, still winterize with antifreeze in case the furnace shuts off for some reason.