Here is the set up I had on my trip with the Rotopax.
There are two in there - one for water on the rear rack and one for petrol at the LHS. These thing are bullet proof so have no fear about mounting them anywhere. I guess you will end up having them on the side of you paniers?
One note of caution - the filler spout is a PITA. They sell an optional one which is hopefully better. Test it and you will see what I mean.
Best of luck!
(And post up the new thread link to the RR once you start it).