Where our discharge vents were just hastily installed pieces of insulated board were there. Large gaps around them and some were never even put in place. Coleman was at the ACA rally last year when our main unit made a noise and seized up.
Three of them pulled the unit loose and replaced the large flat fan and with another set screw so it would never come loose again.
Then they unscrewed all four vents in the coach ceiling. Everyone of them was leaking most off the cold air into the roof area. They used alumanized tape and sealed up all the gaps.
Much of the cooled air was going back into the intakes as they weren't sealed at all either. Some pieces of foil covered fiberglass ducting was just stuck in place. They left big gaps between pieces and duct work.
After the finished the Mh seemed like a meat locker. No more icing up from recirculating cooled air through the intake.
As far as the gaskets between roof and heat pumps or A/C units they screws need to be checked every once in a while. They can loosen and the gasket will shrink too. I think we have had new unit to roof gaskets replaced twice in 12 years.
Last time in a sever rain storm going down the road we could not figure where all the water was coming from. It was the gasket. We tightened the screws and3 it stopped. In Shawnee the Coleman Folks replaced it.