Golfergo-
Here's the scoop.
Ford does not provide a 12V charging line on the F-53 Class A motorhome chassis. They leave that up to the "coach builder"- in your case, Fleetwood.
Some manufacturers do run their own. Our coach has one.
It pains me to say it, but I no longer trust what REV Group (current Fleetwood manufacturer) technical support says about any of their non-current coaches. I could trust them until last February, when they moved the tech support to Indiana, and many, if not most/all, of the old-timers didn't make the move. On my calls since then, they seem anxious to disavow any knowledge or responsibility for information on older coaches.
That's a long-winded way of saying that your coach may have a 12V charge line. A place to look for evidence is in your owner's manual. Page 5-4 shows a hitch connector diagram, and the 12V charge line is called out. The next place to look is inside any fuse boxes Fleetwood provides for chassis-related circuits. You are not interested in any Ford fuse boxes. The owner's manual implies there may be a fuse box inside the outside front compartment. If you can discover such a box, and the cover has a label, it may call out a charge line fuse.
NOTE: Typically, a 12V charge line is ignition-switched; if so, it will only show a signal with the ignition on.
Here is a link to a Google search of iRV2 posts with the terms "2015," "Bounder" and "charge line" in them.
It may seem like too much effort to search for a charge line, but the benefit is that future owners of your coach will not have to figure out what you did.