Which of the following could indicate water damage in an RV?

Visible mold or rot is a clear indication of water damage in an RV. When water infiltrates the structure of the vehicle, it creates a damp environment that fosters the growth of mold and causes wood, insulation, and other materials to deteriorate. The presence of mold is a warning sign that not only confirms water intrusion but also suggests that the moisture has been present for a prolonged period, leading to potential health risks and structural issues.

In contrast, strong engine performance, regular electrical function, and high fuel efficiency do not relate to signs of water damage. These factors pertain to the engine and electrical systems of the RV, which may perform well even in the presence of water damage elsewhere in the structure. Therefore, these options do not provide relevant indicators of water damage within the RV.