When campsites or other organisations ask for your licence plate number - rego or registration number - to make a booking, you can just fill in TBA aka To Be Announced or Rental Vehicle. Then you can let them know your registration number at the time of check-in.

Unfortunately we cannot let you know your registration number in advances as we just don't know it. We only allocate vehicles close to the scheduled pick-up dates as in the world of tourism and travel things can always change unexpectedly.