I guess taking one of the pint sized 2-stroke oil containers and sticking it between the tool box and the bed is the best low tech solution I could come up with. Since the pint bottle is 16 ounces, average fill up is about 16.5 gallons (unless I wait for the light). Close enough for me. Been doing it this way for 50k.
And I pre-mix diesel kleen and 2 stroke, then fill the pint bottle from my stash. One gallon 2 stroke and one bottle of diesel kleen. Almost makes two gallons.
I buy the gallon jugs because its cheaper that way and i just mix my dieselkleen in the funnel on the tailgate.