Greetings from equally tropical Wisconsin. If you are buying fuel locally,its going to be a blend of diesel fuel and kerosene. That should be fine without anti-gel additives down to about -10 deg F. Once fuel is "gelled", no additive will make it any different. It has to be warmed above the point where it gelled. Normally a trip to the shop for a change of fuel filters and a little warm-up indoors works wonders. Remember that failed starting attempts can wash the oil from the cylinder walls. If the compression is marginal you only have a couple of tries to start it with any hope of getting it to run in cold weather.
ASE Master Tech
Mercedes Tech 19 Years