Fuel Temp at normal operating temp?

Does anyone know what temperature your fuel is when driving at normal operating temps. Should I assume that it is close to the air temp outside, or does it heat up a little as some of the unused fuel is sent back to the tank.

Currently I am running a 60-40 mixture of homemade bio (60%) and kerosene (40%) with a dose of LDL. I have run it as low as 12F with no problems but wonder about the temp in the tank.

One Florida TDI'er reported seeing 100 - 110*F using VAG-COM in a warm engine. The fip is heated primarily from conducted heat from the block through the mounting brackets and under hood heat, not returned fuel.
I think you're blend is ok for 12*F, probably better. Try it in your fridge.
If fuel is going to gell, it will do it while parked.

40% Kero seems pretty high. I think you would be fine with a 20% Kero/80% Bio blend.

20% kerosene would probably be ok but that is just because the temps warm up during the day and the fuel in the tank probably never gets below 20F. However, my wife drives the car sometimes with our 2 year old. I would hate for her to get stranded. Also, i am being conservative.

In my 98 Jetta, the IP adds about 25-30F to outside temp.

Which does nothing for you if the car sits for a length of time in the cold. But if you are going heated garage->heated garage....