How should I add insulation to this room that overhangs a porch? – GreenBuildingAdvisor

Climate zone 5 house built in 1995. Two rooms overhang the porch area, and both get very cold at the knee walls that face the porch in winter. I just opened up the porch ceiling and, as you can see in the photos, there is a void, then where the rooms begin there is sheathing, then house wrap (very weird for it to be on the inside of the sheathing, but that’s how the house was made), then fiberglass, then drywall. The floor appears to be 2×6 covered with sheathing, then fiberglass, then the interior floor sheathing.

What is the most reasonable way to improve the insulation, particularly DIY? I’m considering throwing a sheet of polyiso foil faced board over the wall sheathing and then sealing the edges with one part canned spray foam. But I’m worried about creating a moisture trap given the weird placement of the house wrap.

More photos here: https://imgur.com/a/Ta9Ytea