It is not unusual for the ducting to be crushed or kinked (it's typically just vinyl flex hose) or the the exit grate to be stuck closed or maybe plugged with something. RV assembly quality being what it is, anything is possible. Plus, the fan in an RV furnace isn't all that potent and it is not unusual for the end of a duct run to not reeive much air, and what comes out may not be all that hot.
In any case, since the RV is new you should report it to the dealer as a warranty issue and see what they can do. I had severe problems on a new 2002 coach and the dealer was only a small help. Eventually got the attention of an executive of the manufacturer (National RV) at a rally and he sent his lead factory tech guy over to check it out. The tech spent 4 hours and really tore into it. He found two faulty outlets, a partially crushed duct, and removed 4-5 feet of excess duct hose. Flow improved by nearly 50%.
