That green stuff you see on the rear edge of the box is 1/4", foil faced styrofoam commonly used behind steel siding. I cut pieces to fit wherever I could & glued them in place with silicone.
I packed plain old fiberglass insulation between the inner (straight through aluminium) & the outer (c/f) walls of the intake tube.
I saw a pretty slick heat shield/air box made from a rubbermaid wastebasket, I think it was Hotsauce?