Fun tidbits poking around the internet and some loose math.
If you spent $1,000 on an aux fuel tank upgrade, saved 50 cents on every gallon and got 10 mpg towing it would take you 20,000 miles to recoup your investment.
Diesel (according to Mobile and Shell) has a shelf life of 6 months to a year if keep cool and dry. Add biocides and filtration and it will keep longer.
Average weight for a gallon of diesel is 7.0 to 7.3 pounds depending upon blend.
Untreated #2 diesel Gel point is usually around 17.5 °F (?8.1 °C).
Have a great day :)