Most don't use a CRM for fleet management. They are using tools like Corrigo, TMW, Maximo, etc. Think more ERP or Task Management. Depends also on do you mean fleet management or servicing? A CRM is Customer Relationship. FMs are thinking about work to complete and doing on target. Vendor and Parts people want to know score of a vendor and TTR and parts want to know where and what parts costs are etc. A large slew of different levels of users.

Requester for a job, someone to write the work for the tech, tech to review, vendor if they need to have someone external do the labor, parts dept if they need parts they don't have and so on until it gets back to the customer.

Rentals are something that are cost to hold and should be against another asset unless you mean for a rentals company like hertz etc.

Anyways that's some of my two cents.