While wind chill temps have been much colder, the coldest actual temps we have been in this winter have been in the -10F range. We have had no troubles with fuel gelling with the truck main engine, reefer engine or generator engine.
The only thing we have done different from running in less extreme temperatures is use Howe's Diesel Treat, adding it according to the instructions when temps dip below +20F.
We do not have fuel tank heaters on the truck but do sometimes think about adding them. It is possible that someday, we might have a run where we sit for several days, in sub-zero temperatures, with reefer freight on board; and with the generator running to keep the sleeper comfortable, but with no need to run the main engine. Fuel tank heaters might be good to have in such a situation.