The 1st picture shows a tank made with styrene plastic and air tanks from Altas O. The 2nd picture shows a Lionel Geep fuel tank cut in half and styrene added to make it as wide as the Lionel Geep frame.
3rd picture shows a tank made from a rain gutter down spout,
Used the gutter spout and cut it up to get the rounded corners of the fuel tank. The air tanks are wood dowel rod.
The 4th tank is made from styrene .