Unlike our houses, most RVs have plumbing and water lines that run below the floor line and underneath the unit. When temperatures reach approximately 4 degrees Celsius, the plumbing lines exposed to the cold will begin to freeze and expand.
If your water lines have not been emptied of water and protected with plumbing-safe antifreeze, the water inside will expand with no place to go. This leads to cracked lines, connections, and fittings all throughout your RV.
If the hot water tank is not drained properly before storage, the water contained inside can also expand and lead to a cracked tank. In most cases, this requires a complete hot water tank replacement.