Here we have the new hot air path for the duct. We are now exiting under the seat on the outside (or in the pics, at the bottom) rather that the more middle path. That hole had to be filled in.
This new path has to climb or cross over the expanding duct to rejoin its path forwards. Pic 3 gives a pretty good idea.
I had to make duct paths for the join and tape them in separate operations to make all this happen. Thats why I went the straight route the first time. Which blindsidded me to the PAX or GIB space situation.
Nothing easy about this one. BUT its in the past now so I don't care.