Im not familiar with your 5er, but having issues at either end of an rv is sadly quite typical. Firstly its possible that the flexible ducting is badly routed or crushed blocking airflow to your bedroom. It is also possible that the system is poorly designed and more air is balanced to the back of the coach. On the 4 rigs I have owned forced air is pushed out vents according to where they sit in the run. Only owner input is to install a register that closes to "balance" heat somewhat while not restricting it too much and shutting down the furnace due to an overheat situation.
I have only ever had one t-stat, so I am unsure how exactly yours is wired. At first glance I would think its solely for the front a/c and not heat but perhaps I am wrong. I just cant see how 2 t-stats can control a single furnace but hopefully others can validate this.
I believe that your first task is to contact your dealer to have them demonstrate how the hvac is supposed to work to confirm that all settings/features of your furnace and A/C are working. If you can show them that no heat comes out a single duct then they should work on it under warranty.
My honest guess is the furnace is barely large enough for the space and ducts are poorly plumbed and front is not getting what it needs.
On edit, looking at outside photos of a similar unit...it appears your furnace is on the curb side just behind the back wheel. This means your bath/mbr ducts are about as far away from the actual furnace as you can get.
Daryll
