when Nat did his sums, he was accounting for just 1 strap
just use 3 ( or 4 ) X 5 T straps
1 strap from left to right on the FRONT
1 strap from left to right on the REAR
1 strap from front left to rear right
1 strap from front right to rear left
the last 2 in a X shape, you can run it through the tank baffel, then you will have no movement
you have 4 X 5 Tonne straps