Earlier this spring I noticed low air flow to the furnace registers in by Bedroom, which seems opposite of your condition.
During the summer, being curious, I removed an access panel from the side of the cabinet where my fireplace and AV gear is located. I was specifically looking for the furnace so I could se what kind of clearance I had for a modification I have in mind. One thing I noticed is the duct that comes off the furnace plenum and runs to the rear of the coach has about a 1 x 1 tear close to the point where it is clamped to the plenum. This past weekend I used some duct tape to temporarily patch the hose and after my next trip I'll take the coach to the dealer and have then fix the hose under warranty.
US Army (Ret)
2020 Entegra Accolade 37TS
2019 Jeep Grand Cherokee Trailhawk (Toad)
FMCA - F432054