This is the classic problem owners of Diesel engine cars face every winter - the normal summer fuel gels. You will need to make sure you get the right mixture (#1 or #2 I don;t recall which) and you are right kerosene will thin it out. Can you get a tank that can be buried in the yard? Or can you get an outbuilding/shed to put the tank in? Then you could insulate to keep out the cold and run a small electric heater if need be. Heat tape might even do it and it has a built in thermostat.