look at some of the small jap comercials, things like the Mitsubishi supercarry the chassis cab had one that looked about right, the newer ones have those plastic tanks.
never got round to trying it as 2 20l jerrys fit nicely behind the seats with the advantage of being able to jettison the not inconsiderable weight if need be
Mitsubishi Fuso truck by
D70, on Flickr
that sort of thing - not the l200 gaycowboy pickups
(fueltank in red what a service eh!

)