I'm new to towing with a diesel engine, especially in cold weather. We are heading up through northern CA, into Oregon and Wash. In some locations, the temps are dropping into the mid to lower 20's. Is there a need to be concerned about the diesel in the factory fuel tank "jelling"? The owners manual only addresses long term exposure to very cold weather. I believe some locations put an additive in the fuel, but I doubt they do where I live.