Dug a little deeper into the trailer to figure out my next moves.
Wall tubing is 1/2 thick, so that will simplify my insulation choices, pink foam (no blue foam here), here I come! At least 1/2 is quite affordable. My goals here are to remove the tin can sound and keep heat either in or out, depending on what is needed.
All fasteners are SS and over all build quality is excellent. All wire taps are 3M

Couple of niggling things. All the trailer lights wiring follow the same colour coding as the 7pin connector, except for brown that goes into blue. Blue is usually reserved for the trailer brake signal. There is a 4 inch kick panel at the bottom of the walls made of the same plywood as the floor but instead of cutting a brand new sheet, there is one section where they used a small 6-8 inch piece. At least all joints are covered by a niece piece of aluminium.
I took the option to have the inside walls finished, there is nothing wrong with it but definitely not up to my standards. That being said, I knew this was going to be the case and am totally OK with it. I can always re-do it later.

On the good side, everything is easily taken apart, wiring is easily accessible and will be a pleasure to work on!
On the electrical side, for DC (not touching AC, it's fine the way it is for now), everything not trailer related share a single feed and the common is the trailer frame itself. More on
that in the Electrical forum.
Wished I had taken more pictures but I was too busy solving mysteries and making discoveries.