[bestgenman]

I’ve spent over forty years in the generator business and had a small fleet of sets for rent. So, I’ll share forty winter experiences.
This is my opinion which will not be shared by all.  If you search the net for gelling temperatures you’ll see it is all over, but the median point seems to be about ten degrees F for the starting point.  This is where the wax begins to solidify.  Additives can prevent this or at least lower the gel point.  However, water enters into this conundrum. As temperatures change, water condenses and this occurs from the refinining storage tanks clear through the transfer process until it reaches the supply tank for the generator, there’ll always be some water.  The filters are paper, for the most part, and will absorb the moisture, no matter how small.  When fuel passes through the media at below 32 degrees, the moisture trapped by the paper freezes blocking the flow. 
Most diagnoses of gelling are actually frozen filter media not gelling.  The remedy is fuel additives to prevent gelling and plenty of filters.  At the beginning of cold weather, always change fuel filters and carry spares before heading out.
Fleetguard and Racor, to name a few, have in line fuel heaters built into some of their filter heads which are thermostatically controlled to start heating when the temperature drops below their set point.  If there are wires going to your filter head and you don’t have WIF indication, it’s likely for the heating element.  It is rare to seem them in motor coach applications.  

My two cents worth!