Depending on the situation, it may be unclear what exactly caused the breakdown, and the responsibility will be determined by the evidence provided.
If it is not clear whether the damage was caused by a mechanical issue, wear and tear, or another reason, the repair shop where the RV was towed will need to inspect the RV and determine the cause of the breakdown. The shop will be able to assess what happened and provide an explanation and cause for the breakdown in a report.
The party responsible for the breakdown will also be responsible for the cost of repairs.