Close off floor registers?

Its an RV, not the space shuttle. I don't believe there is a lot of high tech work goes into the engineering and installation of the heating system.

The system in our 09 Montana is so unbalanced that the only vent that you can feel air coming out is the rearmost vent, the next vent forward won't blow out a match but you can sort of feel air coming out, the next and last forward vent is in front of the refrig and very little air comes out. Nothing comes out the vents in the bathroom and bedroom.

I looked for balance dampers at the heater and found 5 four inch cheesy foil ducts attached to the plentum with nothing to balance the system anywhere in the system.

You combustion air never contacts your heated circulated air for obvious CO reasons. Slowing and reducing the volume of air will cause the 'exchanger' tubes to over heat. With
possible devastating consequences. Therefore, manufactures put in high temperature shut offs before that temperature can be attained. There are some great electric space heaters out there as a viable alternative.

There is always the option to add a small electric heater to the area where some additional warmth is required.

If I close off the vents in the living room my furnace would run much much longer; that is where the thermostat is. The bedroom would get impossibly hot and I wouldn't be able to sleep anyway. Been there, done that...

I have 6 vents, one being right below the thermostat that really plays havoc with it.

My fix is a magnetic cover from Walmart placed over that one vent. And the picture on the cover, is a vent... :)

when you go camping , don't forget to take your bathrobe. only way you are going to be able to keep warm with our breaking something.

All good information. Glad I asked. Thanks.

Most systems in an RV are so marginal I have to say don't do it. Get a 12v fan to move the air around if needed.

My high limit switch already cycles the burner every few minutes while it heats my trailer due to poor airflow. And I have made improvements over oem install.

Atwood requires a minimum of 30 square inches of unrestricted flow. A 3" duct is 7.06 square inches. Using those numbers, 5 fully open, unrestricted ducts would give 35.30 square inches.In theory any additional registers could be closed. It may not be necessary to totaly close of any registers, only restrict the flow, redirecting it to the desired location.
I would recommend checking the CFM at each register with a flow meter, then closing the desired register/s and check for increased flow at the unrestricted registers.
There are two safety features in the furnace. A sail switch, and high tempperature sensor, of which either can shut down the furnace.
Any good HVAC tech should have a flow meter and be able to test and balance the system.

I wouldn't close any more than one. And not completely. Different registers can be purchased that will allow re-directing air without closing right off.