The security deposit is taken to cover damages that could occur while the renter is using the RV, or to cover additional closeout charges at the return of the RV like extra mileage, propane, generator etc. 

Additionally, if an insurance claim is opened, this deposit will also serve toward the payment of the deductible.

As part of the checklist, make sure to take all the necessary photos before and after the rental to document well the state of the RV to avoid disagreement in regards to additional charges.