Anybody running auxiliary fuel / water tanks mounted on the outside of the frame rails?

I was looking into rotopax but figured it would be more efficient and cheaper to mount plastic tanks up high underneath the vehicle. More capacity, lower center of gravity etc.

 

A water tank, pump, and some sort of heating device (either heat exchanger or tankless propane) is on my todo list. I haven't come up with anything concrete yet though

 

Arb makes some and you have to check their Australian site for them but if I'm not mistaken Devon 4x4 in the U.K. carried em too