Abstract: A mobile storage tank has front and rear walls and a pair of opposing side walls each having ends being in contact with each of the front and rear walls is disclosed. A bottom wall extends from the front wall to the rear wall and abuts the pair of opposing side walls. The bottom wall has a generally flat portion along at least a length portion thereof, and has a curved portion a rest length portion thereof At least the bottom wall is formed having a double ply wall structure in order to prevent leakage of a material contained within the mobile storage tank should an interior wall of the bottom wall become punctured, and further to provide secondary containment.