Another option to consider is a tank from Chev of the 40's. Part #605239 and 605239H. Both are advertised as under the bed units. The first is top fill and the "H" is side fill. I am considering it for my 41 3/4 ton; frame width of 36". Measurements are 27 3/4 x 17 3/4 x 8.5

~ Victor
1941 3/4-Ton Pickup (in process). Read about it in the DITY Gallery
1955 Grumman Kurbside "Doughboy" 235/3 on tree w/ OD
1957 3100 - moved on
1959 C4500 Short Bus "Magic Bus" - moved on
1959 G3800 1 Ton Dually "Chief" - moved on
1958 C4400 Viking "Thor" ~ moved on to fellow Bolter