In 2015, you received your parking permit for the underground car park in the town when you received your documents at registration. But, this caused a problem, where do you park beforehand? So, I parked in the underground car park and got a ticket from the machine as I drove into it and would pay on exit no doubt, if I could read and understand what it said in French on the machine to be able to work it. But, everything sorted itself out, the pass that was issued was for the machine in the car park and it worked with no payment apart for the initial layout of 2 Euro's for the week so I was able to just come and go as I pleased. As Chris Crossland says about PBP "Don't worry about it, everything sorts itself out"
Parking no doubt at Rambouillet will be no different no doubt, somewhere temporary initially by showing your rider number, get your documents and then park in the proper place or just return to the temporary place and stick your pass in the windscreen.