I finally got around to sealing up the air conditioning. Nothing new here, everybody knows exactly what I found when removing the cover. If you didn't know better you might think the manufactures of rv's think tape is a structural building material. Despite all the tape, there was still gaping holes into the attic. I expected to find that. What I did not expect to find was the partition between the supply and return not in place and laying essentially on it's side! The supply and return was entirely open to one another! The only thing meant to hold it in place, you guessed it, foam tape. It appears this is meant to be easily adjustable up and down when adjusting the tension on the gasket bolts.
I found flashing material was easy for me to score, break, and bend by hand. I installed this around the entire perimeter with staples and folded into each duct, then taped accordingly. I even used flashing to seperate between the supply and return.
Air flow has increased dramatically and the unit even seems quieter now.