I did it in my previous company (Yale dealer) and my actual company too. The issue is a little complicated.
Practically the LTR (Long Term Rental) rate consists of two parts: financial and service. Of course the customer is invoiced only for the total rate. The division of the rates is an internal issue.

Of course, everything depends upon the rental conditions, but our LTR contracts include the full service (maintenance, repairs, sometimes tyres and forks). Excluded are only after accident repairs and misuse.
The service part of the LTR rate is based upon the presumed costs.

That's why it's very important to geat all the necessary and detailed info before calculating the rate. These are the yearly/monthly working hours, application, enviromnent, operators skills etc.

We use the detailed tables which show the costs of the different trucks manitenance and service costs basing upon the lenght of the contract, application, yearly working hours etc. And of course the resiudal value of the trucks at the end of the contract.
Then we add some margins and add the values to the financial part of the rate and we get the total rate value.
The service coordinator participates actively in the service rate evaluation.
This service part of the rate is treated as the service income.
The "financial" part of the rate is a sales dep. income.

At the end, if the service guys use too many parts or service hours, the service dep. is on minus.
We link the costs to the trucks (a costs centers) and to the individual technicians. So we can get the plain view of the contract efficiency.