When I worked in Highlevel Alberta Canada, winter time, I saw -46F. The logging camps had diesel stoves for heat and cooking. They would mount the fuel tanks inside the buildings so as to keep the fuel oil liquid.
So, IMO, heating the Racor will have limited if any value if the fuel in the supply tank is very cold.
On your boat, if it is so cold, the fuel is thick, I suspect you have other problems too. It would be better if you installed a block heater or a circulating coolant pump to keep the entire engine and cooling system warm. I used both when I was in Alberta. The advantage of a circulating pump was, start the engine, you have heat in the cab without waiting for the engine to warm up.
The meek will inherit the earth but, the brave will inherit the seas.