Kenneth,
Each cube is 35 gallons. At least the ones I am going to be getting are. So 400 gallons would be 13 cubes. NOT that big a deal size wise. I can't remember overall dimensions, but it MIGHT take up the floor of an M105 and you could put a piece of plywood over that and have TONS of storage.
And DON'T pour it. Get a 12v electric fuel pump and a spare battery (could be charged with solar panel). I've seen them fairly cheap at a couple of auto parts houses here. Besides, just mount a second fuel tank on the truck in the normal position. After running one tank down low, every time you stop to eat or sleep, stick the hose in a cube, flip the switch and 'fill er up'.
That's what I'm hoping for.
jim
Edit - Bjorn, your cubes look a LOT smaller than the one's I'm getting from the resturant that is giving me the oil. Note to self - GO GET ONE CUBE and measure it.