As for the rack, I could find no place on the seat frame to bolt the stabilizing extensions. Improvised with heavy duty cable ties. Still going strong after 7 months and 3 loaded tours.
As for water, I carried 4 liters in collasable bags in that space behind the mesh on my tour in Big Bend, and could have carried 6. Might require a bit of adjustment to the seat position if much is stuffed into that space.