If I give the airborne helicopter a netted load of fuel drums
It was policy Not to carry passengers whilst underslinging loads. Especially with a Whirlwind which couldn't. Two full drums would be a reasonable load but it would have been a waste of time as the helicopter would have used fuel at the same rate as the contents of the drums. Empty drums were OK. You would have been able to carry four as that was all the net would have held.
Go back to Post 7 and the picture of 329. Zoom up and you will see the fuel filler above the bottom pilot's step near the lower/forward corner of the main door. You can see the faint white earthing sign by it.
'Stripped Down'; remove the blast plate.