I put
http://www.fattywagons.com/fwproducts.htm these on my 300SDL prior to my decision not to run WVO. I do run Bio-D and sometimes up to B100, thus, these heaters might still come in handy. Just the other day, my B100 literally froze, but at the time I had sufficient #2 so the fuel did not freeze.
I also found these rather pricey heaters
http://www.vegiecars.com/Injector_Heater/ but even so, I think a heated fuel filter is a necessity, along with a heated fuel system.
The fuel line heaters will get the fuel up to temp quick, verses the slower fuel line systems.