Owners can choose how many kilometers to include in the rental price. When you enter your dates on a listing you will be able to see in the price breakdown how many kilometers are included in the rental as well as the price per kilometer after crossing the limit.
The owner will take note of the odometer when you pick up the RV and do the same when it is returned to calculate any overage charges.
Note that the kilometers are calculated per day, so if you are renting an RV allowing you to drive 200 km per day and your rental is for 3 nights (hence 4 days), the total distance included in the rental will be 800 km. Any kilometer above 800 km will be subject to additional charges are per the listing rate.