Thanks for posting the pictures. The Rotopax seems like a pretty good liquid container since liquid has no shape constraints. However for anything else, the Rotopax design is very inefficient. Having one for fuel and one for water could be a good start towards packing for a 2-3 day back country tour. It would be hard to not find a better choice for the rest of your gear.
Good try Rotopax! Good original design intention, afterthought design idea, not so much.