You need the fuel filter warmed on a diesel. Heating the tank is probably not the best.
You want warmer air going in - heating the water jacket helps with that, intake gets some heat from the cast iron.
You want the oil thin enough to make starting spin faster - again the block heater will warm up the thin films of oil, and slightly heat the oil pan.
A magnetic heater on the oil pan will help with the oil, and slightly get the intake and oil film warmer.
Synthetic or thinner oil helps.
Good battery & fresh starter will spin better.
Adding anti-gel, new fuel filters, using a blend of #1 diesel will all condition the fuel properly.
Just heating the fuel tank is not a good plan. Maybe if you run into an issue it can be part of getting things working again. Actually heating the fuel filter will be the part that helps then... Heating the fuel tank isn't going to offer you much.