So I’m insulating my D2 so I’m taking the headliner out.

I do not have rear jumpers so I’m thinking of modifying the a/c duct work for efficiency to the second row.

Currently planning on making these mods with fiberglass but wanted to get other opinions. I’ve attached a rave pic that illustrates where I’m planning on modifying

 

Sounds like a cool project.
If you're good at laying fiberglass, it should be pretty simple, just time.
Cut the new holes, make whatever pods to hold the ducts, pop rivot pods to headliner board, recover it, done.
The radiant barrier above the headliner will cool things down alot by itself, and having rear ac, the truck should be freezing inside, but I like the idea.
Make it your own, and post pictures!

 

I like the idea of fiberglass, as you can make whatever you want.
But, before I went to the time and effort of that, I would comb some junkyards.
Look in everything, every make and model.
You may see a dash or door panel that catches your eye, and It has the shape you're picturing, you just need to Dremel some duct openings in it.
Or, ducts for rear seats in a console, roof ducts in a minivan, a whole assembly, or trim you can work with.
You could glue, rivot, or nut/bolt it to your headliner.
You may find just the right part(s), or a better idea, once you see it. Junkyards are great for these types of projects.
Who knows, maybe you find nothing...then you can make something out of fiberglass, lol

 

If all you are trying to do is cut then cover the existing vent openings then go ahead and cutout the vents not needed apply duct tape to the opening and apply automotive paste wax to the taped area and duct assembly (this will allow you to remove the patch once cured so you can later trim) cover the area with fiberglass cloth/ mat and resin allow to cure then remove the fiberglass panel and cut to shape. Now you can apply silicone and rivet the new cover panel to the existing plastic vent assembly.

 

Yea that’s all I’m doing. I’m removing the 3rd row a/c by cutting and fiberglassing the hole I cut closed.

im choosing that route because I’m trying to make sure second row air flow is as efficient as possible

 

Some pics for more attention

 

And has anyone figured out what the hell these are for:

 

So the update is, I just simply detached and covered the holes with foil tape and sound deadner. The 2nd row blows a little harder and gets cold faster. So I'd say this was a success.