If your PM is diesel, then inside storage of extra fuel is possible,but if all but assuredly gas. Spare gasoline needs to be stored outside because of any potentially explosive vapors that could escape. Try Rotopax or AT Overland.
Wonder if a safety "fuel cell" (i.e. like those for racing) could be pressed into service? Maybe mounted between frame rails underneath, and plumbed in to the existing fuel tank to increase capacity?
