A dual tank structure includes first and second tanks with a common secondary containment structure which are all integrally supported on a common base frame. The common base frame includes longitudinal skids so as to be suitable for transport using a conventional winch truck. A passageway with an integral valve therein permits selective communication between the tanks. The common containment structure has a containment volume which is greater than a storage volume of a largest one of the first tank and the second tank and which is less than a combined storage volume of both the first tank and the second tank.