Designer 35RLTS and Jayco Talk...Thanks Frank!!

Yes, the second a/c is a 13,500btu unit.

If you want to check the duct, maybe pull off the closest round vent and use a mirror to see what you can see. If you see the insulation then you could use a wire to poke through.

On the sealing of of the supply/return, try a search. But I think if you pull the cover it will be pretty obvious. I have not had to do mine yet, we are getting out this weekend.