Flexible fluid reservoirs with closures and structural members

A fluid reservoir comprising:

• a first sheet and a second sheet coupled together around perimeter edges and defining an internal space between the first and second sheets for fluid storage;
• an upper opening defined between the first and second sheets at an upper end of the fluid reservoir, the upper opening being configured for filling the internal space with a fluid;
• a first plate and a second plate coupled to the first sheet adjacent to the upper opening, the first and second plates being relatively more rigid than the first and second sheets, and wherein the first plate and the second plate comprises pins;
• wherein when the first sheet and the second sheet are closed together to close upper opening and are folded together along a crease extending between the first and second plates with the first sheet overlapping the second sheet, the first plate and the second plate are positioned parallel and opposite each other on either side of the crease with the pins extending outwardly;
• a closure frame configured to be slid over the crease and over the first and second plates with the folded part of the first and second sheets held tightly closed between the two plates by compression pressure from the closure frame, thereby sealing closed the upper opening;
• wherein the closure frame comprises slots that receive the pins of the first and second plates, the slots and pins being shaped to cooperatively prevent the closure frame from sliding horizontally relative to the plates in a direction parallel to the crease;
• and
• a closure lock configured to be attached to the closure frame after the closure frame is mounted over the first and second plates with the pins engaged within the slots, wherein the closure lock blocks at least one of the pins from exiting a respective slot in the closure frame and thereby preventing the closure frame from sliding vertically off of the plates.