I strongly suggest taking guv's advice. In my very limited experience with redcaps, I'm pretty sure I was expected to remain in pretty close proximity to both the redcap and my luggage. I know you're picturing a skycap who takes your bags at the airport and then takes them to be loaded on the plane, but the train doesn't work that way - the redcap takes you and your luggage to the train and loads them in your car near your seats, either in the hat racks or in the luggage racks near the doors.

Also, at that hour, they may simply not be staffed to the point where a redcap could remain with your luggage and your wife while you found somewhere to park the car.