The Tiger 1 had four fuel tanks; one in the rear of each sponson, and another two in the engine compartment. This arrangement dates from the earliest surviving Tiger design drawing.
The fuel tanks in the sponsons were the larger. As these diagrams show, they had a wedge shape. This was because the air inlet duct for the radiator was immediately above.
Each tank was held in place by two metal straps. There were guides for the straps at the top and rear of the tank. The fuel outlet was at the bottom rear.
There was a filler tube at the top of each tank, with a corresponding filler cap in the armoured grille above it. The tube had a rubber seal. This must have been to prevent fuel leakage, not rainwater ingress, because the entire compartment was designed to flood when the Tiger was underwater, and it had a drain.
These are fuel tanks from a Tiger. You can see that the sides of the tank were indented slightly.
The other surfaces of the fuel tank carried a diagonal pattern of bumps. The fuel tank was not painted, so it was presumably made of non-ferrous metal.
[1] Survey of Tiger 250122, at Bovington museum, by David Byrden