my neighbors bought a new Travel Trailer - I walked them through the same process - had them seal and do the rest. I used an anemometer (wind Speed) that I have for the house (to balance out my sticks and bricks HVAC) with my 4 x 10 vent adapter.
When In started, the air speed was 8 mph in the bathroom - and less than 5 in the front bedroom. Taping the inside of the baffle, and stopping the short cycling, it increased to 14 in the bathroom and it was 6 in the front bedroom.
After sealing the vents so no air got in the attic (yes, it was leaking there) cutting the pop in insert that was blocking the airflow in the front bedroom and reducing the volume that could come out of the bathroom, front bedroom was at 12, bathroom was at 6 and the other vents were at 10.
A much better experience, and thanks for the pics and instructions. They were so happy!