each upper flange 20 includes outer and inner flange portions 24 and 26 respectively with 34 outer 34 and 34 inner 34 being referenced to the position of the flange portions relative to the other i beam in like manner each lower flange 22 includes outer and inner flange portions 28 and 30 respectively and a surface 29 which extends across the bottom of the lower flange 22 the longitudinal axes of i beams 12 and 14 such as longitudinal axis 31 of i beam 12 are oriented in spaced parallel relation with one another fuel tank assembly 10 includes a cylindrical fuel tank 32 having first and second axial ends 34 and 36 respectively a curved outer surface or sidewall 38 a longitudinal axis 40 and a top 41 which is the uppermost portion of tank sidewall 38 when tank 32 is properly oriented fuel tank 32 is mounted on i beams 12 and 14 via mounting means 42 and 44 respectively with longitudinal axis 40 of fuel tank 32 oriented transversely to the longitudinal axes of i beams 12 and 14 such as longitudinal axis 31 mounting means 42 and 44 are of like construction and thus only mounting means.