to imgoing4it: I think that you are basically correct in your assessment of the method the Atwood uses. Atwood went to Cormorand and got them to modify the system for the US market and then was bought out by Dometic. Dometic is not really interested in fixing problems with the Atwood because they thought they had a winner in their other pile of offal that they were selling. But they have had so much trouble with it that it looks like everything is going to backfire. This Atwood is quiet and can really put out the heat. If you are having trouble with pulling enough heat out of it, the chances are there is something wrong with the installation.
Look for places where the ducts are blocked or things like that. Try opening the system so that it doesn't use the ducts to see if it does better. If it does, something has gone wrong with the ducts in your coach.