I had the same issue on my trailer.
Unlucky for me, during a trip down to Florida, my underbelly broke free on the front and ripped free back to the axles. Not having time to wait for a mobile tech, I removed the coroplast.
Your ducting is probably the very light weight plastic/foil flex ducting. It is probably installed very loosely. To get best airflow thru this stuff it is supposed to be pulled as tight as possible. As a result, the air flow thru it to the front of the trailer is reduced because of high resistance. Mine was so loose, that were it was not supported by the under belly, it was dragging on the ground.
Because I had complete access, I ripped it all out and replaced 95% with rigid and semi-rigid ducting. As a test, I turned on the furnace and got better but not great airflow to the front. So to further reduce the heat going to the bedroom. I put some aluminum tape on the exhaust port on the furnace port that goes to the bedroom. That should force more heat to where I want it.
The link below goes to another post where I uploaded pictures of the completed ducting. This was before I put wire loom on the wires that were hanging everywhere with minimal support.
http://www.forestriverforums.com/for...ml#post1812178
__________________
Al
I am starting to think, that I will never be old enough--------to know better.
Tolerance will reach such a level that intelligent people will be banned from thinking so as not to offend the imbeciles. Fyodor Mikhailovich Dostoevsky, Russian Novelist
S.E. Mich. Flagstaff 26FKWS / 2022 F-150 3.5 EcoBoost SCrew Propride