Not to beat a horse to death but.....
I’m at the RV and it turnout the plenum that runs from the heater (passenger to drivers) isn’t closed on the driver send - and I can’t feel the passengers side without removing the chloroplast.
So as Time2roll suggested I’ve been crawling around looking for a path to put 4” ducts. It’s going to be ugly but it’s a better option than messing with the plenum under the coach and hoping it works.
Now I wait until I get the upstairs finished and I can remove the stove and get to area to run the duct.
Thanks