"Balancing" motorhome heating systems.

We have had our 2015 Winnebago 36Y since new. We do not shun cold weather camping in our "mobile motel room" and have always been irritated by the bedroom being hotter than the rest of the coach when we sleep at night. This year I decided to go to work to fix this imbalance. I have noticed over the years that on really cold nights when the furnace would run longer times to keep the coach warm that often I would hear the burner shut off while the fan would continue to run until the burner would light again. Comparing this action to the thermostat reading/setting it became obvious that the burner was shutting off due to the high temp limit rather than the thermostat being satisfied. Our Winne has (had) 2 2x12 floor vents, one on the side of the sink cabinet, and a 3" round in the bath cabinet. It became obvious to me that these 4 registers were insufficient venting for the furnace size causing the high limit to activate during long furnace runs. The next problem was the furnace is located in the rear of the coach and the first vent in line was in the bedroom and would provide the strongest flow of hot air. Next in line was the little round bath vent which seemed to provide the proper amount of heat to keep the bathroom comfortably warm. The front half was served by the kitchen cabinet vent and the floor vent that was located right behind the driver/passenger seats. This arrangement made the bedroom get too hot as the two front vents would take too long to warm the front and satisfy the thermostat located in the front of the coach. I began my quest to remedy the problem with the front floor vent. Looking down into it revealed it was time to vacuum the several years dirt out of it anyway. Removing the register, I found the first real design fail. As the duct progresses from rear to front, it shrinks in height. This is in accordance with proper design as they do this to try to balance air flow, the smaller duct at the end of the run produces back pressure to insure the air gets forced out of first few registers and not blow right by on it's way to the end register. At the front end of my coach, the duct is still about 14" wide but down to 2" in height. The first problem I discovered was with the front register itself. None of the registers have "shutters" to adjust air flow, no doubt to prevent people from closing too many and REALLY overheating the furnace due to reduced air flow. The register grate that Winnebago uses, however, still has the internal side plates that the shutter would have been attached to. They extend about 1 1/2" down. Once the register is installed, the combination of those side plates and the shallow, 2" duct means the airflow is further reduced by having to pass through that little 3/4" or so space between the duct bottom and the register side plates. To remedy this, I found the side plates are only attached to the floor plate with double sided tape so I was able to remove them. They really do not add any appreciable strength to the register plate as it is only spanning 2" anyway. Removing the side plates greatly increase air flow out of the front register. I still wanted to increase airflow to the front of the coach to insure the thermostat area would warm quicker and stop the bedroom from getting so hot. Luckily our 36Y has a "peninsula" cabinet in the kitchen area similar to many 5th wheels and that peninsula was over the area of the floor that the duct passed under. I was able to remove the cabinet floor to access the coach floor and then cut a hole through the floor to access the duct. Then I added two registers to the kick panel on each side of the cabinet base. I now have 3 registers on the kitchen cabinet facing forward, left, and right. Reinstalling the cabinet floor created a little plenum that delivered the hot air to my new registers. Now I have much improved airflow to the front half of the coach and am looking forward to heading out in a few days to a local campground to see how well this modification works. Had I not had the cabinet to put the additional registers in, I would have simply put one or two more into the floor like the front one. If you are not satisfied with the distribution of heat in your RV, I suggest you make a similar evaluation of how the manufacturer installed registers in your rig. You may be able to significantly improve the operation by fixing/adding registers like I did.