I also thought about the dampers vents for my 2900, so I bought 3 inch adjustable Damper vent covers to replace the four furnace vents. See attached photos of front and back of butterfly Damper vents.
I don't recall where I got them, maybe etrailer.com,,, but Google comes up with several places that sells them. Search for
3 inch Dampered RV vent
I have three vents in the back (bedroom hallway and bathroom) and only one vent in the front. That front vent is in the kickboard under the kitchen cabinets and it faces the opposite wall of the living room area. Problem with that is... there is absolutely no heat blowing toward the cab in the front. But, I was hopeful that this would fix it. So I installed all them. I adjusted it to the point where some were at 50% open and some at 20% open. It worked well in the driveway. Then after driving a thousand miles to Illinois in December I woke up one night to the sound of an odd whistling noise and I was cold. I found that all of the dampers had loosened up and closed. The air pressure from the furnace was pushing against the butterfly dampers and slammed them shut. I could reopen them and they would close again within 5 or 10 minutes. So in the middle of the night I needed to figure out a way to keep them open. I ended up rolling up some duct tape the right thickness and wedging that into the edge of the butterfly damper to hold it in the position I wanted. I put everything back together and it has worked ever since. I just can no longer adjust the dampers more or less without taking the damper out and moving it by hand. Gave up on inventing a way to tighten the knob to keep them "locked" at a specific position. Maybe someone else has encountered and solved this?
While not totally satisfied with the solution, i looked into what it would take to add another furnace vent in the front of the PC. I needed to install a collar on the manifold of the furnace. I also need ductwork hose and one more event cover. So my options were two or three or four inch ductwork. I didn't quite have room for 4-in to snake through the back of the closet and under the cabinets so I ended up using three inch. Keep in mind that a 2-inch duct only allows about 50% of the air flow of a 3-inch which is about 70% of the air flow of a 4-inch. So the larger the duct work the more airflow you're going to get. Use the biggest you can route under the cabinets.
I've attached a pic of a 4 inch collar as well (I couldn't find a pic of the 3 inch). Every Atwood and Suburban furnace has an air manifold with multiple places to attach air ducts on left front right and top sides. Initially all of the places are blocked with a blank in place and when you need to add a vent you knock out the blank and insert this collar and twist and snap it into place. I actually used aluminum duct tape to seal it and the existing collars as I didn't want air leakage near the furnace. Then attach the air duct on that end, route the duct through the cabinets and add a vent cover on the other end. You'll need a three or four inch hole saw to cut a hole in the cabinet for the duct but it's more difficult finding a place to put the hole than it is to actually doing the work.
You can find the furnace collars in ebay by searching for
(atwood, suburban) furnace collar
I chose to put my new duct in the end of the kitchen cabinets in front of the water heater. The airflow blows out across the entryway toward my recliner and then continues forward and blows warm air into the cab area. A much better result than the dampers. The cab is now warm. The entry step area is now warm.
In my opinion I would suggest adding a vent first, which adds a lot more airflow to the PC than trying to block airflow in the back. Think about it... you probably have two or three vents in the back and only one in the front, right? Adding one more in the front will make a big difference. Also... My halfway vent is just a few inches from the air return grating. All of the hot air was just recirculating back into the furnace. I closed that air vent down to about 20%. That pushes more hot air to the rest of the coach,,, and I think my furnace is quieter now. In retrospect I think the larger coaches (with larger furnaces?) like ours benefit from having another vent. Otherwise they over heat the rear and never warm the front.
Larry
