Reducing return air flow will cause the furnace to work harder and longer. While this will not cause damage to your furnace, it will reduce the life of components and possibly cause high temp limiters to trip. If the unit or furnace is under warranty any modifications will void the warranty. You may have already done so... but I advise you to replace the lost air flow by removing the dummy panel next to it or opening a new panel 50% larger the existing panel at the other end of the cabinet. Keep in mind air flowing through cabinetry will result in dust and debris collecting on items stored in drawers. Like nearly all 5th Wheels, the return air in my DRV Houston is in the steps to the upper deck. While in the main deck living area the furnace is loud enough to interfere with talking and listening to the TV or music. To remedy this I put a return in the half bath wall (five feet from the furnace) 3/4 the size of the original return and a second 10x10 in the upper deck bedroom wall. In the bedroom I simply swapped the shower plumbing access panel with a return vent. Once I was certain I had more than enough return air I blocked up 2/3rd of the return in the stairs and added felt to the hard surfaces under the stairs. This has drastically reduced furnace noise while increasing air circulation on the upper deck. The further you get away from the furnace the bigger the air return grill needs to be to ensure the blower motor is not working harder. The harder it works the lower the RPMs go - reducing air flow through the furnace and out the ducts. The end result is a furnace working harder, running longer to heat the unit. Thus more LP, battery drain (boondocking/grid failure), and short component lifespan. Those with big units like mine can nearly silence their furnace by installing a dedicated return duct in the island via the floor and blocking up the original return with a new panel. A dedicated return duct will require an electric booster to ensure more than enough air flow to the furnace. Theae 12v furnace blowers are not powerful enough to pull air from great distances. Hence return grills being located within a foot or two of the furnace.

That is a great fix. Happy for you. Blessings, Mark Sleppy

Me and the wife dread, putting on the heat in the I5 it is way to loud . Definitely gonna be doing this modification in Dynamax

I can’t believe the Dynamax is louder than the Navion. The Winnebago is raucous. We use a small electric space heater instead if we are camping with hook-ups.

Hope the sound deadening helps! Maybe follow up after you use it some .

Thanks for the video. Could you post a link for the sound panels? You mention them, but I don't see a link.

What size mats did you use?