I like, a lot.
One suggestion, if I may?
I prefer the fuel - where feasible - lower down, for a lower COG a-n-d the spout/filler cap of the RotoPax VERTICAL, for ease of filling/less leaking (Rotopax dont leak, though), etc.
Something more like this, though it needs a frame, but you can still put two on one side (water + fuel).
(either INSIDE a pannier rack, but then it must clear the swing arm arc, or OUTSIDE of the pannier rack, which only adds 8.5cm to the width of soft pannier bags, etc.
Basically, silencers often weigh 6/7/8kg, so 'balancing this weight with say 5L fuel on the other (non-exhaust) side works well...
Just my 5C!
Cheers
Chris & Team