I'm interested in this as well and will be following along to see what you do. I had Dometic ACs on my 2014 - 3850FL. RV Airflow didn't make a kit for the AC on my rig so I made one myself using 1in foam board, reflectix and HVAC tape. That mod cut the noise level in the kitchen by 50% and made a significant difference in the airflow through the duct system.
I will say that the Coleman units are very quiet and I get a consistent 20 degree temp drop at the "blade" vent compared to the return air intake on the AC. One other thing that many people don't notice is the amount of airflow you get when both AC units are running vs only one unit. Since the duct system runs through the entire coach, a single AC running is trying to cool everything and is pushing air from one end of the trailer to the other to do that.
Clark & Peggy
2022 Montana 3791RD
2017 Ford F350, CC, LB, 6.7, 4x4