On my 5er roof drawing (sent from Jayco) it shows three "boxes". Two that say "DO NOT ROUT", which is where they pre-framed and pre-wired for future vents. And one that says "ROUT" which is where their is a factory installed bath fan. At the bottom of the page is "DETAIL A", which is the framing diagram of the three sections that are labeled ROUT or DO NOT ROUT. Those are standard openings sized for roof vents like the Fantastic Fan, Maxxair Fan or the cheap standard one that most RV manufacturers install in the bathroom.
If you only have one of these "boxes" shown on the diagram supplied by Jayco, I would say you only have one place that was planned for a ceiling vent.
I don't know any reason why you couldn't install a Maxxair Fan in the opening you describe. IMO, it would be a good modification. It was for me