I had poor air flow to our bunkhouse slide. That room got a lot colder than the rest of the TT.
After looking it over, I found that I could add another heat vent using a unused output on the heater. It was a straight run of about 3 feet of 4" duct. Then I drilled a 4" hole in the wall to the bunkhouse and installed a adjustable vent.
It cost about $20.00 and 2-3 hours of my time and completely fixed the problem.
Perhaps you may be able to something like this on your TT.
There are many ways that may be possible. For example maybe running another duct from a existing one that has strong airflow etc.
Customizing a TT for the way you want it is part of the adventure to me.
Last year we encounter single digit temps and the limitations of our plumbing in those temps.
So I completely insulated and heat taped all of the plumbing and increased the heat flow and insulation of the enclosed underbelly... We should have running water down to 40 below!