Ok, so no real progress to speak of at this point other than the headliner finally came in and I helped highjack Rob's plywood thread with insulation talk for a couple days.
I bought a $30 box of poly fill from the fabric store to use as lose fill insulation in cavities/ribs. It's just polyester pillow and stuffed animal fill. It was compressed so the 5 lbs is more than enough. Fiberglass and Rockwool is out and I didn't wanna spend the money on thinsulate for that purpose. I used a flexible hard plastic tube to push it into all the hard to reach areas. I'm going cover the entire upper half of the finished walls with headliner and completely cover all the exposed metal of the interior side of the doors and the rear pillars. But I will cut out where there are panels so I can always remove the panels and remove/replace the poly fill to get to wires, mechanisms, tail lights, etc. Or, if the poly fill ends up being crap and I want it out. For $30 and enough to do 2 vans, I figured it's worth trying.
I'm going to glue either poly batting or thinsulate to the walls and then cover the walls floor to ceiling with whole pieces of polyisocyanurate with the reflective side out. Then cover that with Luan, then the headliner. I'm thinking 1" polyiso between the ceiling ribs, then 1/2" over all of it, including the ribs, then Luan, then paint white. I decided against the white corrugated plastic as there's no practical way to fasten it if I cover the ribs with polyiso.
Going to blackout, insulate and cover the rear windows (only windows I have in the back) and run a similar full-time rear camera with separate display, like RV8R posted in the gadget thread.
A pic of the headliner and trying out the poly fill.