Today while making a modification on my Alpine 3640RL (to be posted later with pictures), I made an surprising discovery concerning the heat ducting to the rear living area. Our 3640RL had some heat from the furnace vents in the living area, but not enough air flow to keep the area comfortably warm.
To make modifications, I removed the basement wall panel immediately behind the WaterWorks. The area behind the panel is divided into an upper area that holds most the fresh water plumbing, furnace, central vacuum, etc. The lower area contains the waste tanks, associated heating ducts leading to those tanks, a gnome-sized tunnel leading to the fresh water tank, some electrical, plus the insulated flexible heating ducts that feed the living area.
It was in this lower, waste tank area that I discovered the problem. For some reason, Keystone has most ducts with enough slack that they lay forward with a sharp U-turn to lead to the rear living area. The rightmost of these insulated, flexible ducts made a sharp U-turn to the right above the black water dump valve, passed next to the heavy gauge electrical cable from the rear shore line connection (as it passed to the upper basement to terminate in the recalled transfer switch). And it was here that the problem occured.
The flexible duct was pressed down on to the waste tank basement deck and crushed against the shore line cable as it ascended to the upper basement. The cable was pressing into the flexible duct almost three-quarters of its diameter! The cable was almost closing the duct! Using two 3' dowel rods, I carefully worked the flexible duct, and by carefully pulling and pushing the heavy guage cable from the upper basement, I worked some slack in the cable lead-in such that it lay closer to the port side of the waste sub-basement. This allowed the rising part of the cable to not be so "bowed" towards the starboard and thus stopped pressing the flexible duct closed. I worked an "S" curve into the cable of the upper basement - very carefully! Using the two dowel rods, I pushed some of the extra length of the flexible duct to the port side and flattened the U-turn. I checked that nothing was pressing on any duct work, nor done any damage to any ducts, cables, or systems.
At that point, I went above to the living area, turned on the furnace, and waited. The air flow from the rear-most heating vent was remarkably better!
In fact, the airflow from the kitchen island vent was amazingly improved. I now believe that the airflow from the furnace will now be able to keep the rear living area of the 3640RL at a comfortable temperature.
In other parts of the forum, this problem has been discussed at length. However, the assumption in those other threads was that the heating ducts of the 3640RL was a common duct running the length of the fifth wheel. This is definitely not the case. In fact, the only metal ductwork that I can deduce or see is that ductwork that connects only the bedroom vent to the basement vent! So putting in a air flow limiting vent in the bedroom will not directly impact the air flow of the rear living area. Basically, the (flexible) duct work of the 3640RL resembles a dumped bowl of spaghetti! Limiting the air flow to the bedroom will only increase the airflow to the basement, waste tanks, freshwater tank, and other living areas. But this is useless if the rear living area duct is pressed closed or nearly blocked by a heavy gauge cable.
I would advise caution if anyone decides to "do it yourself" in the same manner I did. If you are not electrically or HVAC inclined, I would encourage you to check this area out for problems, but have a reputable service facility correct the problem.