first off credit where credit is due to trollson for coming up with the initial idea of fuel as cargo here (29th post) :
https://forums.frontier.co.uk/showthread.php/475252-fuel-cargo-hybrid-modules/page2
now on with the post
fuel scoops scoop fuel but what if you could engineer them, what if they could store a certain amount of fuel as cargo after they fill the tanks?
well thats the idea here after the fuel scoop finishes filling your tank based on the engineering grade of the fuel storage mod it stores up to a certain amount as cargo on the cargo rack thereafter (this would require a cargo rack installed and sufficient space to store the fuel cans/bags.)
grade 1: up to 16 tons
grade 2: up to 32 tons
grade 3 up to 64 tons
grade 4 up to 96 tons
grade 5 up to 128 tons
filling would go at the same rate as if it were filling the normal tanks to keep this idea nice and simplistic, once its stored as much as that grade allows or you've run out of cargo space to store it in than it shuts off and fuel scoops 0.00/s just as if the tank is full
while in cargo other than being injected back into the tank its the same as any other cargo, it should also be of no interest to pirates and have no monetary value there